Circular clarifier apparatus and method

ABSTRACT

This application relates to a circular clarifier for separating and removing separable matter, such as suspended solids, from a liquid. The invention may be used, for example, for separating return activated sludge from clarified liquor using a gas flotation process. The clarifier includes a plurality of fluid feed ports for introducing influent into selected treatment cells of the clarifier in a timed sequence, thereby achieving batch flotation of solids or other separable matter in a continuous infeed process. A plurality of spaced-apart, rotating flocculent handling assemblies traverse the treatment cells for sequentially conveying flocculent into spaced-apart, radially extending collection troughs. All of the flocculent handling assemblies may be driven by a single drive means. Each flocculent handling assembly includes a submerged beach and a scraper assembly including a scraper blade which extends upwardly from the beach. The beaches provide a shear plane underneath the surface layer of flocculent. The scraper assembly includes means for lifting the scraper blade in the vicinity of a trough to enable the blade to traverse over the trough and then descend to a position in contact with or proximate to a corresponding beach. Methods of using the clarifier to more efficiently handle return activated sludge or other fragile flocculent are also described. The clarifier may be stand-alone or adapted to retrofit existing circular primary or secondary sedimentation clarifiers.

RELATED APPLICATIONS

This is a Divisional of application Ser. No. 10/801,383, filed Mar. 12,2004 now U.S. Pat. No. 7,258,788.

TECHNICAL FIELD

This application relates to a circular clarifier for removing separablematter from a liquid medium, for example by a gas flotation process. Theseparable matter may include suspended solids, such as return activatedsludge.

BACKGROUND

Clarifiers are well-known in the prior art for separating suspendedsolids from clarified liquor. Most clarifiers operate by sedimentationof solids (i.e. solids sink and are collected from a bottom portion ofthe clarification vessel) or flotation (i.e. solids are caused to floatand are removed as a flotation blanket from the surface of theclarification vessel). Conventional dissolved air flotation (DAF)clarifiers are not typically used in applications where secondaryquality effluent is desired, especially in plants having high flowrates. This is primarily due to the substantial amount of energyrequired for the pressurization of air and recycle water in the reactionchamber. However, in applications where DAF clarifiers have been used,it has been shown that particle sizes from 0.5-500 microns can be easilyseparated from the mother liquor by flotation whereas sedimentationclarification is limited to particle sizes of roughly 50-500 microns.FIG. 1, which is derived from a Water Environment Federation Manual ofPractice¹, compares various treatment technologies for separatingwastewater organics from an influent stream, including sedimentation andflotation clarification. ¹Manual of Practice 8, Design of MunicipalWastewater Treatment Plants, (1991, Vol. I, p. 46)

In practice, most DAF clarifiers are used in applications where highquality effluent is not required. For example, DAF units processing highinfluent solids concentrations have been used extensively in low flowapplications, such as sludge thickeners. Such thickeners produceeffluent quality in the 100 mg/L and greater total suspended solids(TSS) range, even with the use of high doses of polymer. DAF units havealso been used successfully in high flow installations where theinfluent solids concentration is relatively low. However, very few DAFunits are known in the prior art that can process high concentrations ofinfluent solids and also produce high quality effluent without the useof polymers, particularly when such units are loaded at conventionalclarifier design rates.

The flotation separation of biological solids has been successfullyachieved by the inventor using deep vertical shaft bioreactors asdescribed in U.S. Pat. Nos. 5,645,726 and 5,650,070. In deep verticalshaft bioreactors, the entire mixed liquor is subjected to pressure andhence dissolved gas forms not only in the liquid around the biomassparticle but also within the cell wall of the microbes. This makes aportion of the sludge biomass buoyant for a period of time until the gasconcentrations equilibrate across the cell wall. Such bio-flocculentfloats faster and forms a thicker float blanket than flocculent attachedto the surface of the gas bubbles. The float blanket can, however, berelatively fragile and hence care must be taken in separating theactivated sludge from the clarified subnatent.

Most prior art clarifiers exhibit shortcomings in handling fragileflocculent. For example many prior art systems, such as described inU.S. Pat. Nos. 4,279,754 and 5,330,660 employ sloped stationary beaches,the highest point of which, is elevated slightly above the fill level ofliquid in the clarifier bowl. At the back of the beach is a sludgecollection trough that collects the sludge that is pushed by scrapersonto the sloped beach, up the ramp, and into the trough. The top of thetrough is slightly higher than the liquid level in the clarifier toprevent return activated sludge (RAS) flow between scraper discharges.Sludge removal therefore depends on mechanically pushing the sludge upthe sloped beach and into the trough. This action requires a relativelyhighly concentrated (i.e. thick) sludge, a tight scraper-to-beach fitand a mechanically strong sludge float blanket to form in front of thescraper. The sludge float blanket usually needs to be strengthened bythe use of polymers.

Thus, in conventional designs, polymers are used primarily to compensatefor mechanical design limitations, such as aggressive manipulation ofthe biomass using scrapers, ramped beaches and elevated RAS troughsprotruding above the liquid fill level. Ideally, because of cost, theuse of polymers should be eliminated or used only sparingly in secondaryflotation clarifiers. However, if use of polymers is limited, theflocculated float solids that form at the surface of the liquid arerelatively more fragile than floc formed in sludge thickeners using highdosages of polymer.

Krofta has developed various improvements to flotation clarifier design,as exemplified by U.S. Pat. No. 6,174,434. For example, Kroftarecognized the importance of rampless beaches and gravity RAS troughswhen handling fragile sludge blankets. However, the Krofta processdescribed in the '434 patent includes the step of dipping a scoop intothe sludge, thus disturbing the float, and mechanically elevating thescoop so that the sludge will flow by gravity. While this approach is aningenious improvement over prior designs, the Krofta flocculent handlingassembly is mechanically complex and inefficient.

Most flotation clarifiers described in the prior art are rectangular inconstruction. One of the critical parameters in rectangular clarifierdesign is to maximize the width of the beach and the length of theoverflow weir. For example, the overflow weir in a rectangular clarifiermay be double-sided or trough-shaped to maximize its length. The samedesign principles apply in the case of circular clarifiers. However,circular clarifiers can exhibit significant process advantagesespecially when built on a large scale (e.g. 60 feet in diameter ormore). For example, large diameter circular clarifiers provide anopportunity to place the overflow weir along the peripheral wall of theclarifier to thereby maximize its length. Rectangular clarifiers sufferfrom short beach lengths and consequently decreased ability to returnsolids such as return activated sludge. In circular clarifiers, beachesmay be deployed radially to provide a larger effective surface forsludge collection. Also, in circular clarifiers the influent feed may beintroduced from a central, inner portion of the clarifier and effluentmay be removed from the outer perimeter under relatively quiescentconditions.

The need has therefore arisen for an improved circular flotationclarifier capable of achieving a high degree of separation of floatsolids or other separable matter at commercially practical loadingrates, without the use of polymers and without damaging fragileflocculent.

SUMMARY OF INVENTION

In accordance with the invention a circular clarifier for separatingseparable matter from a liquid is provided. The clarifier includes aninfluent supply for introducing the liquid into the clarifier to a filllevel; an outlet for discharging effluent from the clarifier; at leastone flocculent collection trough extending within the clarifierproximate the fill level; and at least one rotatable flocculent handlingassembly comprising a beach movable at an elevation below the trough anda scraper assembly including a scraper blade extending upwardly from thebeach above the fill level. The scraper assembly is movable relative tothe beach to an elevation above the trough when the flocculent handlingassembly traverses past the trough.

In one embodiment of the invention the clarifier may include a pluralityof spaced-apart troughs subdividing the clarifier into a plurality ofliquid treatment regions, each of the treatment regions being definedbetween an adjacent pair of the troughs. In this embodiment the scraperassembly is movable relative to the beach to an elevation above each oneof the troughs when the flocculent handling assembly traverses thereby.

The clarifier may further include a central hub and a peripheral wall,the hub and the wall defining a container therebetween for containingthe liquid. The troughs preferably extend between the hub and the wallat fixed locations. For example, the troughs may be radially extending.

In one embodiment the central hub is stationary and the influent supplycomprises a plurality of spaced-apart influent feed ports for permittingregulated flow of the liquid from an interior of the hub into thetreatment regions. The feed ports may be located at fixed positions onthe hub and may be brought into and out of alignment with movableinfluent inlet ports to open and close the feed ports. For example, theinlet ports may be formed on a first rotatable ring, wherein rotation ofthe first rotatable ring relative to the hub periodically brings thefeed ports into at least partial register with the inlet ports to permitthe introduction of the liquid into the treatment regions. In oneembodiment, rotation of the first rotatable ring is timed so that theliquid is introduced into each of the treatment regions at a locationbehind the direction of travel of the flocculent handling assembly,wherein the liquid in advance of the flocculent handling assembly isthereby maintained relatively quiescent. The feed ports and inlet portsmay be configured so that the liquid influent is introduced into thetreatment regions in sequence. That is, at any given time some of thefeed ports are at least partially open and some of the feed ports areclosed.

The clarifier may include a plurality of spaced-apart flocculenthandling assemblies each rotatable around the hub and driven by a commondrive. Preferably each of the flocculent handling assemblies includes aradially extending beach and a radially extending scraper blade restingon the beach and extending upwardly therefrom. The scraper assemblydisplaces the scraper blade vertically relative to the correspondingbeach in the vicinity of a trough. The clarifier may be configured sothat only one of the scraper assemblies traverses over one of thetroughs at any given time. Preferably the number of the flocculenthandling assemblies differs from the number of the troughs. For example,the clarifier may consist of five flocculent handling assemblies andfour troughs. Each of the flocculent handling assemblies is coupled to asecond rotatable ring rotatable relative to the hub. The first andsecond rings may be operatively coupled together and rotate in unisonrelative to the fixed central hub and the flocculent collection troughs.

The clarifier also preferably includes a holding tank extending withinan interior of the hub and a plurality of flocculent discharge ports incommunication with the holding tank for periodically permittingdischarge of flocculent from the troughs into the holding tank. In orderto facilitate discharge of flocculent, each of the troughs is inclinedtoward a corresponding one of the discharge ports. A hydraulic headdifference is preferably maintained between the troughs and the holdingtank to ensure that the flocculent flows into the holding tank withoutthe use of pumps when a flocculent discharge port is opened. In oneembodiment the clarifier may include an annular outer baffle located inan upper portion of the container in the vicinity of the peripheral walland an inner baffle surrounding the hub, wherein each of the troughsextends radially between the inner and outer baffles and wherein theflocculent discharge ports are formed on the inner baffle. The clarifiermay also include a third rotatable ring comprising a plurality ofspaced-apart flocculent outlet ports, wherein said flocculent isintermittently discharged into the holding tank when the movableflocculent outlet ports are brought into at least partial register withthe flocculent discharge ports. The first and third rotatable rings maybe operatively coupled together and rotate in unison. For example, thefirst and third rotatable rings may consist of portions of a commoncylindrical tube rotatable about the central hub.

The influent supply for introducing influent into the clarifier mayinclude an influent supply chamber in fluid communication with theinfluent feed ports for containing an aerated supply of the liquidupstream from the feed ports. For example, the influent supply chambermay receive a first stream of the liquid influent comprising dissolvedgas from a influent source, such as a deep shaft bioreactor, locatedupstream from the influent supply chamber. The influent supply chambermay be in fluid communication with the holding tank which receivesflocculent from the troughs and optionally recirculates the flocculentto the influent source. Both the influent supply chamber and the holdingtank may be located adjacent one another within the central hub. One ormore fluid recycle ports adjustable between open and closed positionsmay be provided for regulating flow of the liquid between the influentsupply chamber and the holding tank.

The clarifier may further include one or more sediment recycle ports foradjustably permitting passage of any sediment settling in a bottomportion of the clarifier container into the holding tank. Preferably aplurality of rake assemblies each extending under a corresponding beachand rotatable therewith are provided for conveying sediment toward thesediment recycle ports.

Preferably each of the troughs extends a short distance above the filllevel of the liquid within the clarifier container at least part of thetime. Each of the troughs may have the shape of a truncated segment of acircle and include a front edge, a rear edge and a trough bottom surfaceextending therebetween. Each of the beaches comprises an upper surfaceextending in a substantially horizontal plane and movable through thecontainer at a submerged location below the fill level and below theelevation of the troughs. In operation, a surface layer of flocculentforms at the fill level of the liquid within the container, and eachbeach creates a shear plane proximate a lower portion of the surfacelayer as the beach moves through the container. In one embodiment eachbeach has the shape of a truncated segment of a circle and is coupled tothe third rotatable ring rotatable about the central hub. A plurality ofvertically disposed baffles preferably extend outwardly from the thirdrotatable ring between the beaches for regulating flow of the liquidintroduced into the container. An outer weir surrounds the outerperipheral wall for collecting the effluent and conveying it to effluentoutlet(s).

In operation, rotation of the flocculent handling assemblies atlocations between the troughs subdivides each treatment region of theclarifier receiving a flocculent handling assembly into a float subzonein advance of the flocculent handling assembly and a fill subzone inbehind of the flocculent handling assembly. The beach defines the lowerboundary of the float subzone as the beach approaches a next-in-sequenceone of the troughs in the direction of rotation. As the flocculenthandling assembly traverses through the treatment region in question,the float subzone progressively decreases in size and the fill zoneprogressively increases in size, thereby causing at least part of thesurface layer of flocculent to rise above the fill level and gentlyspill over a front edge of the next-in-sequence trough, collecting theflocculent therein. The flocculent handling assembly thereby increasesthe concentration of the flocculent within the float subzone. Each ofthe troughs may include a portion for collecting and discharging a wasteactivated sludge fraction of the flocculent.

A bottom edge of the scraper blade contacts the beach at positionsbetween the troughs. In one embodiment the scraper assembly includes anelongated scraper blade and a vertical adjustment assembly for liftingthe scraper blade in the vicinity of a front edge of a trough andlowering the scraper blade in the vicinity of a rear edge of a trough.The scraper blade therefore traverses substantially all of the exposedsurface of the treatment regions as it rotates within the container. Thevertical adjustment assembly comprises a leading support arm and atrailing support arm each extending between a first end proximate aninner portion of the clarifier container and a second end proximate anouter portion of the container. The vertical adjustment assembly furthercomprises a mechanical linkage coupling the support arms to each otherand to the scraper blade and an actuator for varying the angular spacingbetween the support arms to thereby cause vertical displacement of thescraper blade.

Preferably the scraper blade extends radially between the inner andouter portions of the container, and the scraper blade rotates in afirst arc in a plane of rotation within the container around the hub.The support arms move in a second arc in a support plane parallel to theplane of rotation and extending along a radial axis of the second arc.Preferably the support plane is disposed above the plane of rotation.

The actuator for varying the angular distance between the support armsmay include a cam assembly operatively coupled to the leading supportarm. The cam assembly may include a cam ring mounted on an actuatorsupport structure, the ring having at least one cam surface formedthereon; and a roller coupled to the first end of the first support armand located on an inner surface of a second ring rotatable relative tothe central hub, wherein the roller is movable on the cam surface as thesecond ring rotates relative to the central hub to vary the angulardistance between the support arms. The clarifier may further include adrive for driving rotation of the second ring relative to the centralhub.

The second end of each of the support arms is supported for travel inthe second arc around the clarifier container. For example, the scraperassembly may be adapted for travel over a peripheral outer wall of theclarifier remote from the actuator support structure. In this embodimenteach of the support arms has a roller mounted on the second end thereoffor rolling motion on an upper surface of the peripheral wall.

In one embodiment the second ring comprises at least one slot forreceiving the first end of the trailing support arm. An adjustablelength tie bar may also be provided for coupling the second end of theleading support arm to the second ring. In operation, the relativeangular velocity of the trailing support arm is reduced when the angulardistance between the first and second support arms increases, and therelative angular velocity of the trailing support arm is increased whenthe angular distance between the first and second support arms isreduced.

As indicated above, the scraper assembly is designed to convert rotationof the scraper support arms along a radial line to vertical displacementof the scraper in the vicinity of a trough. In order to achieve thismotion, the support arms may extend in the support plane along radiallines corresponding to opposed truncated edges of an outwardlyprojecting first rhombic pyramid having an apex proximate the first endof the support arms. The linkage connecting the support arms to thescraper blade may include a plurality of first V-shaped first linkageelements extending between the support arms, wherein each of the firstlinkage elements comprises a first segment connected to the leadingsupport arm and a second segment connected to the trailing support arm.Each of the first and second segments are connected together at firstconnectors disposed between the support arms. The connectors are locatedon a radial axis intersecting the first connectors and corresponding toan edge of the first rhombic pyramid located between the opposed edges.Optionally, the linkage may further include a stabilizer shaft extendingalong the radial axis intersecting the first connectors.

The linkage may further comprise a plurality of second linkage elementsfor coupling the first connectors to the scraper. The second linkageelements may include a plurality of spaced-apart second connectors onthe scraper blade, wherein each of the second connectors is (a) coupledto a corresponding one of the first connectors and (b) is located on thescraper blade at a location in a plane extending perpendicular to theplane of rotation and passing through the trailing support arm at alocation where one of the first linkage elements is connected thereto.At least some of the second linkage elements may each further comprise athird connector disposed between the first and second connectors,wherein the third connector is supported for movement in a planeperpendicular to the plane of rotation along an axis intersecting acorresponding one of the first connectors. In a particular embodiment,each of the second linkage elements further comprise third, fourth,fifth and sixth segments together defining a rhombic shape for linkingthe first and third connectors together, wherein the rhombic shapecorresponds to the cross-sectional shape of an inwardly projectingsecond rhombic pyramid having its apex on the radial axis intersectingthe first connectors. A seventh segment may also be provided forcoupling each of the third connectors to a corresponding one of thesecond connectors.

A method of treating influent in a circular clarifier having a containerfor holding the influent and at least one trough extending atapproximately the fill level of the influent is also provided. Themethod includes the steps of introducing the influent into a treatmentregion of the container in the vicinity of the trough; causing afraction of the influent comprising separable matter to form a surfacelayer of flocculent in a flotation subzone of the treatment region; andconfining the flocculent within the flotation subzone while graduallydecreasing the volume of the flotation subzone to cause the flocculentto rise above the fill level and gently spill into the trough withoutsubstantially disrupting the flocculent. The clarifier preferablycomprises a rotatable flocculent handling assembly as described aboveand the step of gradually decreasing the volume of the flotation subzonecomprises rotating the flocculent handling assembly through thetreatment region.

Although influent is introduced into the clarifier containercontinuously, flocculent is floated in different treatment regionssequentially in a batch-like process. According to the method, eachtreatment region is operable in a fill phase, a float phase or acombination fill/float phase. Rotation of the flocculent handlingassembly through the treatment region subdivides the region into theflotation subzone in advance of the direction of travel of the assemblyand a fill subzone behind the assembly. The liquid influent isintroduced into the fill zone of the treatment region, but not the floatsubzone, during the fill phase and the fill/float phase.

In another embodiment of the invention a circular flotation clarifierfor separating separable matter from a supply of liquid influent isprovided comprising a container for holding the liquid; a plurality oftroughs extending in the container at spaced-apart locations, whereinthe troughs each extend at approximately the surface level of the liquidin the container; a plurality of spaced-apart beaches rotatable relativeto the troughs within the container at an elevation below the troughs;and a plurality of scraper blades, each of the blades extending upwardlyfrom a corresponding one of the beaches and being rotatable therewith,wherein the scraper blades subdivide the container into a plurality ofrotatable liquid treatment cells, each of the treatment cells beingdefined between two of the scraper blades. More particularly, each ofthe treatment cells is defined between a leading scraper blade and atrailing scraper blade and is movable past each of the troughs insequence in a direction of rotation.

The liquid is introduced into each one of the treatment cells during afill period commencing when the leading scraper blade passes the rearedge of one of the troughs and ending when the trailing scraper bladepasses the rear edge of such trough. Each of the treatment cells may besubdivided during the fill period into a fill subzone between theleading scraper blade and the trough and a float subzone between thetrailing scraper blade and the trough. As the treatment cell rotatesaround the clarifier container relative to the trough, the fill subzoneexpands in size and the float zone contracts in size. The treatment cellis not in fluid communication with the influent supply chamber during adwell period commencing when the leading scraper blade passes the frontedge of the trough and ending when said leading scraper blade passes therear edge of the trough.

Each of the feed ports described above in communication with the fillsubzone is at least partially aligned with one of the movable influentinlet ports during the fill period to permit introduction of the liquidinfluent into the fill subzone during the fill period. Since influent isnot introduced directly into the float subzone during the fill period,the mixed liquor or other liquid is substantially quiescent within thefloat subzone in advance of the trailing scraper blade as it rotates inthe direction of rotation. Depending upon the position of a specifictreatment cell relative to the troughs, the fill subzone or the floatsubzone may comprise the entire treatment cell; at other locationsduring rotation of the treatment cell, the treatment cell may besubdivided into separate fill and float subzones as described above.

BRIEF DESCRIPTION OF DRAWINGS

In drawings which illustrate embodiments of the invention, but whichshould not be construed as restricting the spirit or scope of theinvention in any way,

FIG. 1 is a chart comparing treatment technologies for separatingwastewater organics of varying particle size and molecular mass.

FIG. 2 is an isometric view of the Applicant's circular clarifier in itsassembled configuration.

FIG. 3 is an exploded, isometric view of the clarifier of FIG. 2 showingthe clarifier subassemblies.

FIG. 4 is a simplified cross-sectional view of a functional model of theclarifier of FIG. 3.

FIG. 5 is an isometric, fragmented view of the clarifier bowlsubassembly.

FIG. 6 is an isometric view of the lower rotating subassembly.

FIG. 7( a) is an isometric, fragmented view of the flocculent troughssubassembly.

FIG. 7( b) is a first isometric view of a flocculent collection trough.

FIG. 7( c) is a second isometric view of a flocculent collection trough.

FIG. 8( a) is an isometric view of the upper rotating subassembly.

FIG. 8( b) is an enlarged perspective, fragmented view of a portion ofthe upper rotating subassembly releasably coupled to the lower rotatingsubassembly.

FIG. 8( c) is a series of schematic plan views showing a shutter forautomatically adjusting the flocculent discharge port timing sequencedepending upon the selected position of the scraper blade positionrelative to the beach.

FIG. 9 is an isometric view of the scrapers drive, cam ring andoperator's platform subassembly.

FIG. 10 is an enlarged, isometric view of the scraper subassembly.

FIG. 11 is an enlarged sectional view of the scraper subassembly of FIG.10 engaging the front edge of a flocculent collection trough.

FIG. 12 is a simplified isometric view of the scraper subassemblyshowing the scraper blade in a lowered position.

FIG. 13 is a simplified isometric view of the scraper subassembly ofFIG. 12 showing the scraper blade adjusted to a raised position.

FIGS. 14( a)-14(e) are simplified isometric views showing an exemplarygeometric arrangement of the scraper blade and scraper support arms forconverting rotation of the support arms to vertical displacement of thescraper blade in the vicinity of a flocculent collection trough.

FIG. 15 is a simplified plan view showing the position of the influentfeed ports, flocculent discharge ports and flocculent collectionconduits relative to the troughs subassembly.

FIG. 16 is a simplified plan view showing the relative position of theinfluent inlet ports and flocculent outlet ports relative to the beachesand baffles of the lower rotating subassembly.

FIG. 17 is a simplified plan view showing the rotating structures ofFIG. 16 superimposed on the fixed structures of FIG. 15 at a selectedtime period.

FIG. 18 is simplified plan view showing the structures of FIG. 17 at alater period in time showing the lower rotating subassembly rotated by asegment of 9°.

FIG. 19 is simplified plan view showing the structures of FIG. 17 at alater period in time showing the lower rotating subassembly rotated by asegment of 18°.

FIG. 20 is a simplified plan view showing the bottom recycle port timingrelative to a rotating shutter ring.

DESCRIPTION

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive, sense.

Invention Overview

This application relates to a circular clarifier 10 for separating andremoving separable matter from a liquid medium. The separation may beachieved, for example, by a gas flotation process. Other processesrelying on the differential density of the separable matter and theliquid medium may also be employed. The gas flotation or otherseparation process causes at least a portion of the separable matter toform a layer on the surface of the liquid medium within clarifier 10. Asdescribed herein, the separable matter, such as a surface layer offlocculent, is collected and discharged from clarifier 10 for downstreamprocessing or recirculation to an upstream component, such as bioreactorsupplying liquid influent to clarifier 10. The liquid influent maycomprise suspended solids or other separable matter.

As used in this patent application “separable matter” means any matterdispersed, suspended or otherwise present in a liquid medium and whichis separable from the liquid, such as by gas flotation clarification.The separable matter may include solids, liquids or gases present in theliquid medium in any form whatsoever. For example, the separable mattermay comprise suspended solids, colloids and emulsions. The invention iseffective in separating and removing separable matter which is notordinarily removable from the liquid medium by conventional filtration(i.e. non-filterable residue). Suspended solids may include biomassparticles such as return activated sludge. By way of further example,the separable matter may include color colloids, macro molecules,surface active solids, liquids and gases, minerals and oil emulsions,such as tar sands pond water. As shown in FIG. 1, flotation separationcan potentially remove particulates down to about 0.01 microns in size.The separable matter may also include larger floatable materials, suchas offal, hair, feathers and the like (which may be ordinarilyfilterable by other means).

As used in this patent application “flocculent” means any separablematter concentrated in a surface layer of the liquid medium. Forexample, the flocculent may comprise a float blanket comprisingsuspended solid particles which are caused to rise to the surface of theliquid medium by a gas flotation process. Although, the invention isdescribed herein in the context of gas flotation of suspended solids, itshould be understood that the invention could be applied for separationand removable of non-solid flocculent, such as liquids or gases,concentrated in a surface layer of the liquid medium.

As used in this patent application “gas flotation” refers to the processof dispersing and/or dissolving a gas in a liquid medium by any means.For example, the process may involve dissolving air, a mixture of gasesor a pure gas in the liquid medium. Alternatively, the gas or gasescould be produced within the liquid medium by chemical reaction(s). Forexample, in the case of a process for the removal of phosphorus,flotation may be achieved by acidification of the mixed liquor with alumor ferric chloride. This results in the release of carbon dioxide whichis then used for the purposes of flotation. In another example, purenitrogen gas may be used in refinery applications to separate oil fromwater.

As should be apparent from the foregoing, the terms “clarifier” and“clarification” as used herein are not restricted to a process forremoving solid particles from a liquid. Rather, such terms refer toapparatus and process for removing any separable matter (includingnon-solid matter) from a liquid medium in accordance with the invention.

As shown in FIGS. 2 and 3, clarifier 10 of the present inventionincludes five different subassemblies which are operatively coupledtogether, namely a clarifier bowl subassembly 100, a lower rotatingsubassembly 200, a flocculent troughs subassembly 300, an upper rotatingsubassembly 400 and a scraper drive, cam ring and operator's platformsubassembly 500. As described further below, lower and uppersubassemblies 200, 400 rotate in unison relative to subassemblies 100,300 and 500 which remain fixed in place during operation of clarifier10.

Clarifier Bowl Subassembly

As shown best in FIG. 5, clarifier bowl subassembly 100 includes aclarifier bowl 102. Bowl 102 comprises a cylindrical liquid treatmentreservoir 104 defined between a central cylindrical hub 106 and aperipheral wall 108. A floor 110 forms the bottom surface of reservoir104. A tapered apron 112 may be provided for securing hub 106 to floor110. This feature is shown in cross-section in FIG. 4 which illustratesa functional model of the invention. Bowl 102 also includes an outereffluent overflow weir 114 defined between peripheral wall 108 and anoutermost cylindrical wall 116. Weir 114 has a bottom surface 118 havingone or more discharge outlets 120 formed therein for enabling flow ofeffluent from weir 114 into a discharge conduit 122.

Central hub 106 includes a holding tank 124 defined by an innercylindrical wall 126, in an upper portion thereof, and an intermediatewall 136 in a lower portion thereof, as shown best in FIG. 8( b). One ormore sumps 128 are formed in or proximate to apron 112 for collectingsettled solids from a bottom portion of reservoir 104 and recycling theminto holding tank 124 (FIGS. 4 and 5) as described in further detailbelow. A conduit 130 extends upwardly within the interior of holdingtank 124 to provide access to the upper portion of hub 106 and otherinterior components of clarifier 10. For example, conduit 130 providesfor easy routing of services such as air, cleaning water, polymer,instrumentation cables and the like.

Hub 106 further includes an influent supply chamber 132 defined betweenan outer wall 134 and intermediate wall 136. A plurality of influentfeed ports 138 are formed in outer wall 134 to permit regulated flow ofinfluent from chamber 132 into liquid treatment reservoir 104 asdescribed below. In the illustrated embodiment, influent feed ports 138are shown as being rectangular. However, in alternative embodiments feedports 138 could be other shapes or configurations which would have theeffect of altering the fluid flow dynamics. A discharge valve 140 isprovided in a bottom portion of chamber 132 for purging any solids whichsettle therein.

An internal recycle overflow weir 142 is located within the interior ofhub 106 between an upper portion of holding tank 124 and influent supplychamber 132 (i.e. weir 142 may comprise an upper portion of intermediatewall 136 as shown best in FIG. 8( b)). Weir 142 includes a trough 144having one or more recycle ports 146 formed in a flat bottom portionthereof. One or more float valves 148 are disposed within tank 124 forregulating recycle flow through ports 146 from weir 142 into tank 124(FIG. 5). Float valves 148 help maintain a head difference betweenreservoir 104 and holding tank 124 to eliminate the need to pumpflocculent into tank 124 as described below.

Clarifier bowl subassembly 100 includes a plurality of conduits fordistributing fluid to and from central hub 106. For example, central hub106 may be in fluid communication with an upstream bioreactor (notshown), such as a hyperbaric vertical shaft bioreactor described in U.S.Pat. No. 5,645,726, the disclosure of which is hereby incorporatedherein by reference. In the illustrated embodiment, a deep extractionline 150 originating in a saturation zone near the bottom of theupstream bioreactor and a shallow extraction line 152 originating in thehead tank of the upstream bioreactor convey influent into influentsupply chamber 132. In this arrangement the deep extraction line 150supplies influent containing mostly dissolved gas and the shallowextraction line 152 supplies influent containing dispersed gas or microbubbles. The rate at which the influent is introduced into influentsupply chamber 132 may vary depending upon the size of supply lines 150,152. Preferably influent is introduced into influent supply chamber 132in a manner sufficient to cause a turbulent flow of influent therein.For example, the outlets of supply lines 150, 152 may be orientedtangentially as shown in FIG. 5 to induce a counter-clockwise flow ofinfluent within chamber 132. The outlet of the deep extraction line 150may be disposed immediately above the outlet of shallow extraction line152 to allow the dispersed gas to travel upwardly through the dissolvedgas stream. Accordingly, the two influent streams co-mingle in theinfluent supply chamber 132. As described in Applicant's '726 patentreferred to above, the fluid mixture of dispersed gas at atmosphericpressure causes the much greater quantity of dissolved gas, at thehigher partial pressure, to come out of solution just prior to itsintroduction into reservoir 104. This results in a homogenous mixture ofbubbles and suspended solids (or other separable matter) within influentsupply chamber 132 which is an important requirement for good gasflotation separation. The influent mixture is delivered from chamber 132through feed ports 138 into reservoir 104 for flotation as describedbelow. The influent may be introduced into reservoir 104 through feedports 138 so as to induce liquid flow in a direction opposite to theflow direction in influent chamber 132 (e.g. clockwise rather thancounterclockwise).

By way of example, influent may be introduced into chamber 132 throughsupply lines 150, 152 at a rate of approximately 3-6 ft/sec in the caseof small clarifiers 10 and approximately 10-15 ft/sec in the case oflarge clarifiers 10. Depending upon the size of clarifier 10, thehorizontal velocity of influent within chamber 132 may be maintainedwithin the range of approximately 1.5 to 2.5 ft/sec, thus substantiallypreventing settlement of solids. However, any solids which do settlewithin chamber 132 may be purged through valve 140. In this example thesize of feed ports 138 are configured so that an entry velocity intoreservoir 104 of 8-10 ft/minute, at average daily flow, is maintained.This ensures proper energy levels for flocculation of the incoming mixedliquor influent. Further, due to the upflow of bubbles liberated wheninfluent passes through feed ports 138 into reservoir 104, a sufficienthead loss is created to ensure substantially equal fluid flow within theappropriate treatment regions 600 of clarifier 10 as described below. Inthis example the residence time in the active volume portion of influentsupply chamber 132, namely the volume of chamber 132 above supply lines150, 152 but below feed ports 138, is less than one minute. This allowssufficient time for large bubbles, which may be disruptive to theformation of the float blanket, to escape from the top of the influentsupply chamber 132 and not enter reservoir 104. As will be apparent to aperson skilled in the art, this example is for illustrative purposesonly and many variations are possible without departing from theinvention. For example, although the influent liquid is described hereinin the context of a mixed liquor comprising suspended solids, otherliquid influent could be introduced into reservoir 104 as describedabove.

As shown in FIGS. 5 and 8( b), clarifier bowl subassembly furtherincludes a plurality of spaced-apart, laterally extending flocculentcollection conduits 154. As described below, conduits 154 conveyflocculent from troughs subassembly 300 (FIG. 7( a)) into holding tank124 of clarifier bowl subassembly 100. A seal 156 is provided at theouter end of each conduit 154.

Influent is preferably delivered through supply lines 150, 152 intoinfluent supply chamber 132 continuously. In one embodiment of theinvention raw influent may also be delivered through a supply line 158directly into holding tank 124. Further, the contents of holding tank124 may be recycled to an upstream reactor through a recycle line 160(FIG. 5).

As described in detail in Applicant's '726 patent referred to above,optimum air flotation performance is achieved when influent isintroduced into reservoir 104 at a relatively constant rate and where aminimum delivery time has elapsed between the upstream influent sourceand reservoir 104. If pressure regulation valves are not used, the rateof gas dissolution is a function of time and is generally linear withdistance. For example, the distance between the zone of maximum gassaturation in the upstream reactor to feed ports 138 could be 300 to 400feet in a small clarifier 10 and 400 to 500 feet in a large clarifier10.

In order to ensure a relatively constant flow of influent into reservoir104 under varying operating conditions, an internal recycle stream isprovided which is conveyed through recycle line 160. The recycle streamis equal to the difference between the flow volume to the point ofdelivery through feed ports 138 and the forward flow of effluent througheffluent discharge conduits 122. In one embodiment the recycle stream isalso equal to the influent or effluent flow plus a waste activatedsludge (WAS) component. In other words, the infeed influent flow ratemay be equal to the rate of removal of effluent and WAS from clarifier10 to maintain constant fluid flow within the system. In order toaccomplish this, holding tank 124 and treatment reservoir 104 arehydraulically coupled. In particular, when the influent flow rate intoholding tank 124 through supply line 158 exceeds the effluent flow ratethrough discharge conduits 122, the liquid level in holding tank 124rises which causes closure of ports 146 by float valves 148 (FIGS. 5 and8( b)). This is turn causes decreased flow over weir 142 and increasedflow to effluent discharge conduits 122. Conversely, when influent flowis less than effluent flow, the fluid level in holding tank 124 willdecline causing increased flow over weir 142 (FIG. 8( b)) and reducedflow to effluent discharge conduits 122.

By way of example, the maximum internal recycle rate may be set at twicethe average daily flow. Influent flows in excess of the twice averagedaily flow may be accommodated by increasing flow in influent supplyline 152 which is controlled by the head tank level in the upstreaminfluent source. The length of the overflow weir 142 may be determined,for example, by an allowable overflow rate of 50,000 gallons/day/linearfoot of weir at average daily flow.

Solids settling on the bottom floor 110 of reservoir 104 may be conveyedinto holding tank 124 from sumps 128 through standpipes 162 (FIG. 5).Flow may be increased or decreased by adjusting the height of standpipes162. Standpipes 162 may optionally be fitted with air lifts to clearblockages. As shown best in FIG. 5, each standpipe 162 includes an inletport 170 in communication with sump 128. In one embodiment, opening andclosing of port(s) 170 may be adjustably regulated as described below.

Holding tank 124 therefore contains a mixture of fluids and solids fromvarious sources. In particular, conduits 154 intermittently conveyflocculent into tank 124; conduit 158 conveys raw influent into tank124; ports 146 and valves 148 regulate the flow of the internal recyclestream into tank 124 from weir 142; and sumps 128 and standpipes 162convey bottom recycle into tank 124 as described above. The resultingmixture is discharged from a bottom discharge port 163 of tank 124 intomixed flow recycle line 160.

A narrow track 164 is formed on an upper outer surface of wall 134 andextends peripherally around central hub 106 (FIG. 5). As describedfurther below, track is provided for rotatably coupling the lowerrotating subassembly 200 to the stationary clarifier bowl subassembly100.

Lower Rotating Subassembly

FIG. 6 illustrates the lower rotating subassembly 200 in detail.Subassembly 200 is rotatable relative to subassembly 100. Subassembly200 includes a cylindrical support cylinder 202. In the illustratedembodiment, a plurality of rollers 204 extend inwardly from an upperportion of cylinder 202 at spaced intervals. Rollers 204 travel on track164 extending peripherally on wall 134 around central hub 106 ofclarifier bowl 102 thus enabling cylinder 202 to rotate relative to hub106 (FIG. 2). As described further below, rotation of cylinder 202 maybe driven by a drive means disposed above subassembly 200 andmechanically coupled thereto.

Subassembly 200 also includes a plurality of spaced-apart rollers 205extending outwardly from an upper portion of cylinder 202 for rotatablycoupling subassembly 200 to trough subassembly 300. A plurality ofcut-outs 207 may be formed in an upper edge of cylinder 202 to enableservicing of rollers 204, 205. In one embodiment, the upper edge ofcylinder 202 also includes upwardly projecting plate sections 209located in regions between cut-outs 207 for aligning lower rotatingsubassembly with upper rotating subassembly 400. An alternative meansfor adjustably coupling lower rotating subassembly 200 to upper rotatingsubassembly 400 is shown in FIG. 8( b).

Cylinder 202 includes a plurality of spaced-apart influent inlet ports206 formed therein. As cylinder 202 rotates relative to hub 106, inletports 206 are periodically brought into alignment with feed ports 138formed on hub 106, as described in detail below. Movable inlet ports 206thus regulate flow of liquid from influent supply chamber 132 intoliquid treatment reservoir 104. As is the case with feed ports 138, thesize and shape of inlet ports 206 may vary depending upon the desiredfluid flow dynamics.

Cylinder 202 also includes a plurality of spaced-apart flocculent outletports 208. In the illustrated embodiment, each flocculent outlet port208 is positioned directly above an influent inlet port 206 althoughother configurations are possible. As cylinder 202 rotates relative tohub 106, movable flocculent outlet ports 208 are periodically broughtinto alignment with flocculent discharge ports 312 formed in troughsubassembly 300 (as described below) and flocculent collection conduits154 (FIG. 5) This permits discharge of flocculent collected in a trough306 through aligned ports 208, 312 into holding tank 124. The size andshape of ports 208, 312 may vary without departing from the invention.

A plurality of horizontally extending beaches 210 are cantilevered offcylinder 202. Each beach 210 includes an upper surface 212 a chamferedleading edge 213 and a chamfered trailing edge 214. A channel track 216is located at the outer end of each beach 210. Track 216 engages rollers328 of subassembly 300 as described below to guide beach 210 undertroughs 306. As used in the patent application, the term “leading”refers to the portion of beach 210 which leads in the direction ofrotation and “trailing” refers to the portion of beach 210 which trailsin the direction of rotation. In use, chamfered leading and trailingedges 213, 214 provide an air pocket under beach 210. Such air pocketsreduce the effective dead weight of beach 210 and related supportstructures and prevent sludge from sticking to the bottom surface ofbeach 210. As described further below, since dissolved air is typicallycoming out of solution in reservoir 104, there is a small flow of airconstantly being emitted from under each beach 210.

A plurality of baffle assemblies 218 are also cantilevered off cylinder202. Each baffle assembly is located between a pair of the beaches 210and includes canted mid-radius baffles 220 and outwardly extendingskewed baffles 222. Skewed baffles 222 extend between cylinder 202 andmid-radius baffles 220. Baffles 220, 222 direct the flow of liquidentering reservoir 104 through ports 138 as described below.

A plurality of rake assemblies 224 are also cantilevered off cylinder202. Each rake assembly 224 is located below a corresponding beach 210and includes rake plows 226 which move through a bottom portion ofreservoir 104 as cylinder 202 rotates around hub 106. As describedbelow, rakes plows 226 move solids which settle on the bottom floor 110of reservoir 104 toward sumps 128 formed in apron 112 (FIG. 5). In theillustrated embodiment, the rake plows 226 of each rake assembly 224 aremounted on a rake 227. Rake 227 is supported below a corresponding beach210 by a first support arm 228 connected to cylinder 202 and a secondsupport arm 230 connected to an outer end of beach 210.

In order to provide enhanced structural support, cylinder 202 mayinclude an upper stiffening ring 232 extending around the periphery ofcylinder 202 immediately beneath feed ports 206 and a lower stiffeningring 234 supporting rake arm 227. A plurality of portals 236 may beformed in cylinder 202 between stiffening rings 232, 234 to lighten theweight of cylinder 202. Portals 236 also reduce the risk of sludgebuild-up between cylinder 202 and central hub 106.

As will be appreciated by a person skilled in the art, in alternativeembodiments of the invention cylinder 202 could be subdivided intomultiple annular portions or rings which are operatively coupledtogether. For example, movable influent inlet ports 206 could be formedin a first ring and movable flocculent outlet ports 208 could be formedon a second ring disposed above the first ring. The first and secondrings could be coupled together to rotate in unison.

As shown best in FIG. 6, lower rotating subassembly 200 may also includea lower peripheral shutter ring 240 comprising a plurality of elongatedshutters 242 of varying height. Shutter ring 240 rotates in unison withlower rotating cylinder 202. As described below, this causes shutters242 to alternatively close and open standpipe inlet ports 170 in oneembodiment of the invention. Thus the amount and timing of bottom solidsmaterials recycled back to holding tank 124 may be regulated.

Troughs Subassembly

FIGS. 7( a)-7(c) illustrates troughs subassembly 300 in detail.Subassembly 300 includes an inner baffle 302 which is positionableoverlying hub 106 and an outer baffle 304 which is disposed proximate toperipheral wall 108 of clarifier bowl 102 (FIG. 2). As described below,inner baffle is supported on hub 106 via rollers 205. Outer baffle 304has a track 305 formed on its upper surface. A plurality of spaced-apartflocculent collection troughs 306 extend radially between baffles 302,304. Each trough 306 has a relatively narrow inner end 308 and a widerouter end 310 and may have the shape of a segment of a circle. Aplurality of flocculent discharge ports 312 are formed in inner baffle302 proximate an inner end 308 of a respective trough 306. In theillustrated embodiment, each trough 306 has a front edge 314, a rearedge 316 and a bottom surface 318 inclined downwardly from outer end 310toward inner end 308 to facilitate passage of a return activated sludge(RAS) component of flocculent (for example) through discharge ports 312.As used in this patent application, “front edge 314” refers to the edgeof a selected trough 306 that upper rotating assembly 400 firsttraverses as it rotates around hub 106 (for example, in a clockwisedirection) and “rear edge 316” refers to the edge of the selected trough306 which upper rotating assembly 400 traverses after it has traversedover the width of trough 306. As shown in FIG. 11 and described below,front edge 314 may be a composite structure comprising, for example, anassembly of seals, spacers and support surfaces.

Each discharge port 312 has a stationary seal 320 formed on its innersurface as shown in FIG. 7( a). As best shown in FIGS. 7( b) and 7(c), awaste activated sludge (WAS) hopper 322 is located within trough 306 forcollecting WAS. As described below, the WAS is discharged into WASdischarge lines 132 rather than through discharge ports 312.

Subassembly 300 is coupled to subassembly 100 in a fixed position (andis therefore not rotatable relative thereto). Inner baffle 302 includesan upper rim 311 which serves as a track for receiving rollers 205, thuspermitting lower rotating subassembly 200 to rotate relative to bothsubassemblies 100 and 300 (FIG. 6). As subassembly 200 rotates, movableflocculent outlet ports 208 are periodically brought into alignment withflocculent discharge ports 312 to permit flow of RAS or other flocculenttherethrough into flocculent collection conduits 154 (FIG. 5). Conduits154 empty into holding tank 124 as described above. As cylinder 202rotates, it passes between seal 320 located on the inner surface offlocculent discharge port 312 and seal 156 on the outer surface of acorresponding flocculent collection conduit 154. Seals 320, 156compensate for any out-of-roundness of rotating cylinder 202.

In one embodiment seals 320, 156 may be asymmetrical about theircenterline. Accordingly, when seals 320, 156 are manually inverted theeffect is to change the flocculent discharge timing. Other means foradjusting the timing of flocculent discharge ports 312 are describedbelow and illustrated in FIGS. 8( b) and 8(c).

As shown in FIG. 7, subassembly 300 may also optionally include aconical skirt 324 extending inwardly from outer baffle 304 below troughs306. Skirt 324 is used when very high quality effluent is required. Inthis event, support arm 230 (FIG. 6) may function as a plow to removeany solids which may accumulate on conical skirt 324.

Outer baffle 304 may include a plurality of vertical vanes 326 toprovide structural support as shown in FIG. 7. One or more adjustablerollers 328 may be provided on outer baffle 304 for adjusting theelevation of beach 210. In particular, each roller 328 engages beachtrack 216 to adjust the elevation of beach 210 and ensure that a wiper329 (shown in FIG. 11 and described below) functions properly. Eachroller 328 is mounted eccentrically on a plug 330 formed in outer baffle304. The plug may be rotated with a handle 332, thereby adjusting theelevation of roller 328. Plugs 330 are removable from outside outerbaffle 304 for servicing.

Upper Rotating Subassembly

FIGS. 8( a)-8(c) illustrates upper rotating subassembly 400 in detail.Subassembly 400 includes a support cylinder 402 which is coupled tocylinder 202 (FIG. 2) and is rotatable therewith. As will be appreciatedby a person skilled in the art, various means for operatively couplingcylinders 202, 402 together so that they rotate in unison may beenvisaged. One particular embodiment is illustrated in FIG. 8( b) and isdescribed below. In another embodiment, cylinders 202 and 402 mayalternatively comprise sections of an integral torque tube rather thanseparate subassemblies.

A ring gear 405 is located on the inner circumferential surface ofsupport cylinder 402 for driving rotation of cylinder 402 (and cylinder202 which is coupled thereto). As described in detail below, ring gear402 is coupled to a sprocket 503 driven by gear motors 502 and/or 504(FIG. 9).

Support cylinder 402 supports rotation movement of a plurality ofscraper assemblies 406. Each scraper assembly 406 includes a radiallyextending scraper blade 408 and a scraper blade support and liftingmechanism 410 for supporting and lifting blade 408 above a correspondingbeach 210 (FIGS. 8( a) and 10). As described in detail below, supportmechanism 410 is designed to lift blade 408 when assembly 406 traversespast the front edge 314 of a trough 306 and to lower blade 408 when ittraverses past the rear edge 316 of a trough 306 as assembly 406 rotateswithin clarifier bowl 102. In one embodiment support mechanism 410comprises a leading support arm 412 and a trailing support arm 414 whichextend radially in a support plane above the plane of rotation ofscraper blade 408. As used in the patent application, the term “leading”refers to support arm 412 which leads in the direction of rotation and“trailing” refers to the support arm 414 which trails in the directionof rotation. Scraper blade 408 is connected to support arms 412, 414 bya linkage 416. Rollers 418 are mounted on the outer ends of support arms412, 414 for travel over the upper edge 305 of outer baffle 304 (FIGS. 2and 7). An adjustable length tie bar 420 extends between supportcylinder 402 and the outer end of leading support arm 412 to provideadditional structural support (FIG. 8( a)).

The inner end of trailing support arm 414 is slidable coupled to supportcylinder 402. In particular, each trailing support arm 414 is movablewithin a corresponding slot 422 formed in support cylinder 402 to enableadjustment of the angular distance support arms 412, 414 as describedbelow. A roller rocker wheel 424 is mounted on the inner end of eachleading support arm 412 within the interior of support cylinder 402(FIG. 8( a)). As described below, wheel 424 traverses a scraper liftingmechanism actuating cam 512 to actuate adjustment of the angulardistance between support arms 412 and 414 (FIG. 10) and hence verticaldisplacement of scraper blade 408 in the vicinity of a trough 306.

Details of Scraper Blade Lift Mechanism

FIGS. 10-14 illustrate scraper blade support and lift mechanism 410 infurther detail. Mechanism 410 mechanically converts rotational movementof support cylinder 402 to vertical displacement of support blade 408 inthe vicinity of troughs 306 as described below. Rotating movement ofscraper blade 408 along a radial axis is temporarily discontinued duringthe period blade 408 is raised and lowered. Due to the relative spacingof troughs 306 and scraper assemblies 406, in the illustrated embodimentof the invention only one blade 408 is vertically displaced at anyselected time while the other blades 408 continue to rotate in a commonplane of rotation at a constant velocity (all of the scraper assemblies406 are preferably driven by a common drive). Linkage 416 connectingsupport arms 412, 414 to blade 408 is configured to achieve thesepurposes. As shown best in FIG. 10, linkage 416 includes a plurality ofV-shaped first linkage elements 426 extending between first and secondsupport arms 412, 414. Each element 426 includes a first segment 428connected to leading support arm 412 and a second segment 430 connectedto trailing support arm 414. Linkage segments 428, 430 are joined byfirst connectors 432. Optionally, first connectors 432 may be connectedtogether along a stabilizer shaft 434.

Linkage 416 further includes a plurality of second linkage elements 436for coupling first connectors 432 to second connectors 438 which arelocated on blade 408 at spaced-apart locations (FIGS. 12 and 13). Atleast some of the second linkage elements 436 disposed toward the innerend of support arms 412, 414 (and toward the outer end of arms 412, 414in the case of the embodiment of FIG. 14( e)) further include thirdconnectors 440 located between first and second connectors 432, 438. Inthis case, second linkage elements 436 include third, fourth, fifth andsixth segments 442, 444, 446 and 448 which together define a rhombicshape for linking first and third connectors 432, 440 together. Further,a seventh segment 450 may be provided for linking the second and thirdconnectors 438, 440 together. Linkage 416 may further include astabilizer link 451 for supporting blade 408 relative to trailingsupport arm 414 (FIG. 10). In one embodiment, best shown in the enlargedscale of FIG. 11, segment 450 may include a lower portion 453 forcoupling segment 450 to a tapered bottom portion of scraper blade 408.

In a preferred embodiment of the invention scraper blade 408 is raisedand lowered in a vertical plane in the vicinity of a trough 306. Inorder to achieve such movement, support arms 412, 414 preferably extendin a support plane above scraper blade 408 along radial linescorresponding to opposed edges 460 of an outwardly extending, truncatedfirst rhombic pyramid 462 having an apex 464 located proximate the innerends of support arms 412, 414 (FIGS. 14( a)-(e)). First connectors 432(and stabilizer shaft 434 if one is provided) also preferably extendalong a radial axis corresponding to an edge 461 of rhombic pyramid 462.Further, each second connector 438 is located in a vertical planepassing through the trailing support arm 414 at position where secondsegment 430 is connected thereto (FIG. 14( c)). Each third connector 440is located on a vertical axis intersecting one of the first connectors432. Further, the rhombic shape defined by third, fourth, fifth andsixth segments 442, 444, 446 and 448 corresponds to the cross-sectionalshape of an inwardly projecting second rhombic pyramid 466 having itsapex on the radial axis of stabilizer shaft 434, as best shown in FIGS.14( b)-14(d). This geometric linkage arrangement causes true verticaldisplacement of scraper blade 408 along its radial line as the angulardistance between support arms 412, 414 varies, as described below.

FIG. 14( e) illustrates the geometric relation of an alternativeembodiment of the scraper blade support and lift mechanism 410 which isparticularly well-suited for scraper blades 408 which are very long inlength (e.g. clarifiers 10 of very large diameter). In this embodiment athird projecting rhombic pyramid 468 (i.e. in addition to first rhombicpyramid 462 and second rhombic pyramid 466) is shown in dashed lines.Rhombic pyramid 468 has an apex located on an edge of first rhombicpyramid 462 (for example, on a radial axis corresponding to stabilizershaft 434) and notionally projects outwardly within pyramid 462. Bycontrast, second rhombic pyramid 466 has an apex located on an edge offirst rhombic pyramid and projects inwardly externally of first pyramid462. In the embodiment of FIG. 14( e), the apices of pyramids 466, 468are at the same location (corresponding to the location of a firstconnector 432 in a central portion of mechanism 410).

As should be apparent to a person skilled in the art, rhombic pyramids462, 466 and 468 of FIGS. 14( a)-14(e) are provided to more clearly showthe geometric and spacial relationship between parts of the scraperblade support and lift mechanism 410 enabling vertical displacement ofscraper blade 408 while still permitting rotation of mechanism 410 alonga radial line. Pyramids 462, 466 and 468 are presented for the purposesof illustration and do not necessarily correspond with specificstructural parts of a working assembly.

FIG. 11 illustrates the physical relationship between a beach 210 and ascraper blade 408 as beach 210 begins to slide underneath a flocculentcollection trough 306. As indicated above, in one embodiment of theinvention front edge 314 of trough 306 may be a composite structurecomprising various seals and plates. In particular, composite front edge314 may comprise a metal wall 315 coupled to a stepped weir plate 317and a cover plate 319. A spacer 323, which allows for clamping pressureon weir plate 317 as described below, is also disposed between coverplate 319 and wall 315 underneath weir plate 317. The various componentsof trough front edge 314 are held in place with fasteners 321. In otherembodiments of the invention trough front wall 314 may have a unitaryrather than a composite structure.

In the embodiment of FIG. 11, weir plate 317 has a plurality of stepsformed therein. Depending upon the amount of flocculent flow required,any one of the step configurations may be chosen to control the degreeof flocculent overflow into trough 306. Thus weir plate 317 isadjustable to control the effective height of trough front wall 314 atparticular locations along its length. For example, weir plate 317 maybe adjusted to preferentially permit portions of the float blanketformed within clarifier reservoir 104 to spill into an adjacent trough306.

A flexible wiper 329 is loosely contained between cover plate 319 andwall 315 underneath spacer 323. Wiper 329 is prevented from falling outof containment by a pin 331 or other suitable fastener. In theillustrated embodiment, pin 331 extends through an aperture formed inwiper 329. As shown in FIG. 11, wiper 329 is preferably positionedvertically by a tapered ramp 215 formed at the leading edge 213 of beach210 such that wiper 329 lightly contacts upper surface 212 as beach 210travels under trough 306.

In operation, scraper blade 408 rests on or proximate to beach 210 untilit engages front edge 314 of trough 306 whereupon it is liftedvertically as described above. As shown best in FIG. 11, scraper blade408 may include a lower seal 470 for sealingly engaging blade 408 tobeach 210. An adjustable wiper 472 may also be provided for sealinglyengaging blade 408 to cover plate 319 (i.e. the outermost portion oftrough front edge 314) during the period when blade 408 is liftedvertically. The position of wiper 472 is adjustable to ensure thatscraper blade 408 will sealingly engage cover plate 319 irrespective ofthe exact orientation of trough 306.

Seal 470 and wipers 329 and 472 may be formed from a soft elastomericmaterial, for example. Other means for achieving sealing engagement maybe envisaged by a person skilled in the art.

In the embodiment of the invention illustrated in FIG. 11 an adjustablepin 474 is provided for releasing clamping pressure on flexible wiper472. In operation, as beach 210 and scraper blade 408 advance together,they eventually come in contact with cover plate 319 of trough frontedge 314 and a loosely fitting seal is formed between flexible wiper 472and cover plate 319. The scraper lifting mechanism then moves upward asdescribed above allowing a cross bar 478 on pin 474 to contact wiper 472thereby locking it in the appropriate position with respect to coverplate 319. Wiper 472 remains locked in that position until scraper blade408 again contacts beach 210. This allows wiper 472 to conform to thecover plate 319 of the next-in-sequence trough 306 (which typically willrequire a somewhat different positioning of wiper 472).

Wipers 329 and 472, and seals 323 and 470, may be sectioned into 8-10foot long lengths, for example, for ease of handling, installation andrepair. The sectioned lengths may be reversible and interchangeable.Typically wiper 329 clears, or substantially clears, the end of beach210 just as wiper 472 begins its vertical rise. Thus, for any one trough306, just one wiper 329, 472 is in frictional engagement with itscorresponding mating surface. (This assumes that scraper blade 408 is inthe “full bite” position shown on the left-hand side of FIG. 8( c); ifthe scraper blade 408 is in the “half bite” position shown in theright-hand side of FIG. 8( c) or some other modified position, bothwipers 329, 472 may be in frictional engagement simultaneously duringpart of the scraper blade lift cycle).

Clarifier 10 is configured to limit the frictional drag resulting fromthe operation of wipers 329, 472 and seal 470 in other respects. Forexample, in the illustrated embodiment only one of 5 wipers 472 isengagement with a corresponding trough front edge 314 at any given time.

In practice, ease of servicing wipers 329, 472 is important. Inaccordance with the invention, the scraper blade support mechanism 410can be stopped in the “up” position with a blade 408 above a trough 306.By rotating a retainer thumb latch 494 upward, adjustable pin 474 can beremoved. This in turn releases scraper blade 408 and wiper 472. One ofthe two vertical pins on each stabilizer link 451 may be pulled to allowblade 408 to be completed decoupled from support mechanism 410. Onceblade 408 is removed, seal 470 may be easily serviced. As will beapparent to a person skilled in the art, servicing can be accomplishedwith very little tooling. Moreover, if any tools or parts are dropped byservice personnel, they will be captured within a trough 306 and willnot fall into clarifier reservoir 104.

During servicing, the scraper assembly 406, with blade 408 removed, maybe rotated until beach 210 just begins to contact the next-in-sequencetrough 306. Fasteners 321 may then be undone to permit cover plate 319to be removed. Stepped weir plate 317 and wiper 329 may then be easilyremoved for servicing. As mentioned above, by positioning a beach 210 inclose proximity to trough 306, no component parts will fall intoclarifier reservoir 104 during servicing.

The point of rotation between support mechanism 410 and scraper blade408 is labelled 492 in FIG. 11. Rotation point 492 should preferably belocated as close as possible to plate 319 to maintain the correctgeometry of the lifting mechanism as described above. Rotation point 492is ideally located directly below the center-line of trailing supportarm 414.

Adjustment of Scraper Blade Position Relative to Beach

An important feature of the invention is that the landing position ofeach scraper blade 408 on a corresponding beach 210 is adjustable toalter the capacity of clarifier 10. As described below, in order for theflocculent discharge ports 312 to open, a scraper blade 408 approachinga trough 306 in the direction of rotation must be in contact with orproximate to the upper surface 212 of a corresponding beach 210. Thecloser the contact point of scraper blade 408 to trough 306, the smallerthe entrapped volume or “bite” of flocculent, such as RAS, and hence thesmaller the batch discharge.

As discussed above, the flocculent outlet ports 208 are formed on thesame cylinder 202 which supports beaches 210. Therefore, advancing orretarding the landing spot of the scraper blade 408 on beach uppersurface 212 effectively changes the relationship of scraper blade 408 toan outlet port 208. Adjustment may be accomplished by lifting cylinder402 relative to cylinder 202 along a part line between the two portionsand adjusting the relative position of the cylinders. Moving scraperblade 408 forward or rearward on beach upper surface 212 effectivelychanges the active area or forward exposure of beach 210 which in turnproportionally changes the volume of flocculent discharged into a trough306 as indicated above.

One means for incrementally adjusting the relative positions ofcylinders 202, 402 is shown in FIG. 8( b). In this embodiment at leastone flange 211 is coupled to cylinder 202. Flange 211 is alignable witha corresponding flange 409 mounted on cylinder 402. Flanges 211, 409each include a plurality of apertures 217, 413 arranged at spacedintervals. One or more connector pins 415 may be inserted throughapertures 217, 413 for releasably coupling flanges 211, 409 (and hencecylinders 202, 402) together in the desired orientation. Apertures 217,413 may be drilled in a vernier pattern, for example, to enable fine,incremental adjustment of the relative position of cylinders 202, 402.In one embodiment apertures 217, 413 may be arranged to permit a maximumadjustment corresponding to the width of one trough 306

The embodiment of FIG. 8( b) is configured so that adjustment of therelative position of cylinders 202, 402 may be readily accomplishedmanually without the need for special tools or training. In order tomake such an adjustment, connector pin 415 is removed and theforward/backward “jog” button on the drive motor is actuated to causerelative motion of cylinders 202, 402. Alternatively, the relativeposition of cylinders 202, 402 may be adjusted manually. Since uppercylinder 402 is relatively lightweight in comparison to lower cylinder202, the cylinders will slide easily relative to one another alonglubricated flanges 211, 409. As shown in FIGS. 8( a) and 8(b), a shutterplate 496 is mounted on upper cylinder 402 which changes the effectiveposition of the trailing edge of the flocculent outlet port 208 as lowercylinder 202 is indexed relative to upper cylinder 402. That is, shutterplate 496 may be adjusted to alter the effective size of a flocculentoutlet port 208 (FIG. 8( b)) and hence the timing of opening and closingof a corresponding flocculent discharge port 312 (flocculent dischargeport 312 is opened when it comes into partial alignment or register withan outlet port 208).

This feature is best shown in FIG. 8( c). The sequence of drawings onthe left-hand side of FIG. 8( c) shows in schematic plan view a beach210 and scraper 408 assembly moving relative to a stationary seal 320.Seal 320 is mounted on a flocculent discharge port 312 at the inner end308 of trough 306 (FIG. 7( a)). As explained above, flocculent flowsthrough a discharge port 312 into a flocculent collection conduit 154and thereafter into holding tank 124 of clarifier bowl subassembly 100.Seal 156 is provided at the outer end of each conduit 154 as shown inFIGS. 8( b) and 8(c). Seals 320 and 156 compensate for anyout-of-roundness of rotating cylinder 202 in a manner similar to a diskbrake caliper of a motor vehicle. Seal 156 is held in place by means ofthe liquid head that is imposed on it (due to the liquid headdifferential between the clarifier reservoir 104 and holding tank 124).Although seals 320, 156 are stationary, cylinders 202, 402 rotaterelative thereto and hence the seals effectively function as slidingseals.

In operation, rotation of cylinder 402 is actuated by a sprocket 503(FIG. 8( b)) driven by a motor 502 as described further below. Sprocket503 engages a ring gear 405 located on the inner circumferential surfaceof cylinder 402. Rotation of cylinder 402 in turn causes rotation ofshutter 496 attached thereto. In the middle, left-hand panel of FIG. 8(c), beach 210 has rotated 18° until the scraper blade 408 extendingupwardly from the beach trailing end 214 contacts the front edge 314 oftrough 306. Further rotation of cylinders 202, 402 through an arc of 18°causes blade 408 to be lifted upwardly as described above. In themeantime, flocculent discharge port 312 closes as shown in the bottom,left-hand panel of FIG. 8( c).

FIG. 8( c), right-side, shows the same sequence of movements of thescraper blade 408 and beach 210 assembly in an embodiment where blade408 has been adjusted to a “half bite” position contacting beach uppersurface 212 in a central region thereof rather than at the trailing end214. This is accomplished as described above by changing the relativeposition of cylinders 202, 402 which in turn changes the position ofshutter 496. As shown best in FIG. 8( c) shutter 496 remains inalignment with scraper blade 408 so that port 312 is fully open whenscraper blade 408 contacts the front edge 314 of trough 306. Shutter 496effectively closes port 312 when further rotation of cylinders 202, 402(i.e. through an arc of 18°) causes blade 408 to be lifted upwardly to aposition suitable for traversal over a trough 306. Thus shutter 496alters the effective size of port 208 which in turn alters the portopening/closing timing of port 312.

As should be apparent to a person skilled in the art, at all selectedindex settings the flocculent discharge port 312 is designed to beginopening when the leading edge 213 of the beach 210 meets the front edge314 of a flocculent collection trough 306 or shortly thereafter. Byattaching shutter 496 to the upper rotating cylinder 402 which moves thescraper blades 408, and by forming flocculent outlet ports 208 in lowerrotating cylinder 202, the timing of the opening and closing of theflocculent discharge ports 312 is automatically adjusted to accommodateany desired position of scraper blade 408 on beach 210. For example, asshown in FIG. 8( c), discharge port 312 is fully open when scraper blade408 contacts the front edge 314 of trough 306 and fully closed whenblade 408 is fully raised above trough 306 irrespective of whether blade408 is in the “full bite” (left-hand side) or “half bite” (right-handside) orientation. Thus the timing of discharge ports 312 isself-adjusting—when the position of the scraper blade 408 is alteredrelative to beach 210, the timing of opening and closing of a dischargeport 312 is automatically adjusted due to the altered position ofshutter 496.

Flocculent Discharge Cycle

In operation, trough 306 contains dilute flocculent remaining from theprevious cycle at the beginning of a flocculent discharge cycle (i.e.when port 312 begins to open). This is desirable to prevent thickenedflocculent “hang-ups” between batches. That is, if the flocculentcontained within a trough 306 becomes overly viscous between discharges,it could interfere with the proper orientation of ports, seals or othersystem components. As soon as the leading edge 213 of beach 210 contactsthe front edge 314 of trough 306, port 312 begins to open (i.e. port 312begins to come into alignment with a moving port 208 formed on cylinder202) thereby permitting rapid flow of dilute flocculent into holdingtank 124. As trough 306 empties, thickened flocculent is displaced fromthe float subzone (defined by beach 210, scraper blade 408 and frontedge 314 of trough 306) into the interior of trough 306. As indicatedabove, the position and orientation of stepped weir plate 317 (FIG. 11)may be adjusted to regulate the flow of flocculent into trough 306. Forexample, weir plate 317 may be oriented to preferentially permitflocculent flow from particular regions of the float blanket formed inthe float subzone upstream from trough 306.

Thickened flocculent collected in trough 306 continues to be dischargedfrom trough 306 through flocculent discharge port 312 until continuedrotation of cylinders 202, 402 causes scraper blade 408 to contact frontedge 314 of trough 306. At this time scraper blade 408 begins itsvertical travel while beach 210 and flocculent outlet port 208 continueto rotate, causing flocculent discharge port 312 to gradually close.Flow into trough 306 is blocked by scraper blade 408 which is moving ina vertical direction along the front edge 314 to trough 306 as describedabove. By the time the scraper blade 408 reaches the top of its travel,flocculent discharge port 312 is now fully closed. Scraper blade 408then traverses above trough 306 and trough 306 fills with diluteflocculent drawn from the area behind (i.e. upstream) of front edge 314of trough 306 (i.e. from the right to the left direction in the drawingof FIG. 7( c)). This treatment region of clarifier 10 is now in the fillpart of a “fill, float, draw” cycle. The rear edge 316 of trough 306 ispreferably of sufficient height to prevent any flow of flocculent, mixedliquor or other liquid to be clarified thereover. The ability to closethe flocculent discharge port 312 during the period that flow intotrough 306 is blocked by scraper blade 408 is important—this preventsunwanted “short-circuiting” of dilute flocculent directly into trough306 and through discharge port 312 into holding tank 124

Scrapers Drive, Cam Ring and Operator's Platform Subassembly

FIG. 9 illustrates the scrapers drive, cam ring and operator's platformsubassembly 500 which is fixed in position relative to subassembly 100.Subassembly 500 includes an electric gear motor 502 for driving rotationof lower and upper rotating subassemblies 200, 400. Preferably both ofsuch subassemblies are actuated by a common drive. For example, motor502 may drive rotation of a sprocket 503 which engages ring gear 405located on the inner circumferential surface of support cylinder 402 foractuating rotation thereof (FIG. 8( b)). Since cylinder 202 is coupledto cylinder 402, both cylinders (and their attached assemblies describedabove) will rotate in unison.

An emergency, low horsepower output gear motor 504 may also additionallybe provided, such as a small air drive or gasoline/diesel motor. Anoperator platform 506 and servicing deck 508 are provided for operatoraccess to motors 502, 504 and scraper assemblies 406. As shown in FIG.2, servicing deck extends radially above scraper blade support mechanism410. The torque delivered by motor 502 to cylinder 202 may besubstantial. For example, in a medium sized clarifier 10 the torque willbe on the order of 200,000 to 300,000 pound-feet and may exceed 500,000pound-feet in the case of large clarifiers 10.

Subassembly 500 further includes a cam ring 510 having a plurality ofactuating cams 512 formed therein. Each cam 512 includes a sloped firstshoulder 514, a horizontally-extending surface 516 and a sloped secondshoulder 518. Wheel 424 mounted at the inner end of each scraper leadingsupport arm 412 rotates around cam ring 510 and traverses each cam 512.As shown best in FIGS. 10 and 12-13, as wheel 424 traverses firstshoulder 514 of cam 512, the angular distance between leading andtrailing support arms 412 and 414 increases due to stoppage (ordeceleration) of trailing support arm 414 thereby causing upwardvertical displacement of scraper blade 408. Thus vertical displacementof scraper blade 408 is actuated by cam 512 transmitting torque toleading support arm 412 which in turn causes support arms 412, 414 tospread apart (FIG. 10). As wheel 424 moves along surface 516, blade 408is maintained in the elevated position (i.e. above a correspondingtrough 306). As wheel traverses second shoulder 518 of cam 512, trailingsupport arm 414 accelerates and the angular distance between supportarms 412, 414 decreases, causing scraper blade 408 to be displaceddownwardly to its usual operating position resting on or proximate to anunderlying beach 210. During the vertical displacement of scraper blade408 described above the other scraper assemblies 406 coupled to cylinder402 continue to rotate at a constant velocity.

Port Timing Sequence

FIG. 15 is a simplified, plan view of a circular clarifier 10 havingfour equally spaced, stationary, radially extending flocculentcollection troughs 306. Each trough 306 covers an 18° segment ofclarifier 10. A plurality of liquid treatment regions 600 are definedbetween adjacent pairs of troughs 306. In the illustrated embodimenteach treatment region 600 covers a 72° segment of clarifier 10. Eachtreatment region 600 receives a supply of mixed liquor (or other liquidto be clarified) through fixed influent feed ports 138 from influentsupply chamber 132 located with central hub 106. As described above,central hub 106 also includes holding tank 124 for receiving flocculentfrom troughs 306 through flocculent discharge ports 312 and flocculentcollection conduits 154. Feed ports 138 are periodically brought intoalignment with rotating influent inlet ports 206 and flocculentdischarge ports 312 are periodically brought into alignment withrotating flocculent outlet ports 208 (rotating ports 206, 208 are notshown in FIG. 15). In FIG. 15, stationary ports 138 and 312 are shown inconcentric arrangement for the purposes of clarity. However, in oneembodiment of the invention, ports 138, 312 may be superimposed ornearly superimposed above one another when clarifier subassemblies 100and 300 are coupled together and hub 106 may have a constant diameter.

FIG. 16 is a simplified, plan view of lower and upper rotatingsubassemblies 200 and 400 which rotate around central hub 106 asdescribed above. In the illustrated embodiment lower rotatingsubassembly 200 includes five radially extending beaches 210. Liketroughs 306, each beach 210 covers an 18° segment of clarifier 10. Asdescribed further below, the number of beaches 210 differs from thenumber of troughs 306 to enable discharge of flocculent to holding tank124 in timed batches (i.e. the discharge loading is intermittent).

As described above, each scraper blade 408 extends upwardly from thetrailing edge 214 of a corresponding beach 210 and rotates in unisontherewith (in a clockwise direction as denoted by the arrow in FIG. 16).A plurality of liquid treatment cells 610 (labeled A, B, C, D and E inFIG. 16) are defined between adjacent pairs of scraper blades 408 (andadjacent pairs of beach trailing edges 214). Each treatment cell 610therefore covers a covers a 72° segment of clarifier 10. Since beaches210 and scraper blades 408 are rotating around clarifier reservoir 104,the position of treatment cells 610 changes during operation ofclarifier 10. FIG. 16 also includes a simplified showing of influentinlet ports 206 and flocculent outlet ports 208 which are formed onrotating cylinder 202. In FIG. 16 moving ports 206 and 208 are shown inconcentric arrangement for the purposes of clarity when in fact they maybe superimposed above one another as shown in FIG. 6 (i.e. they may beboth formed on cylinder 202).

In the illustrated embodiment, each flocculent outlet port 208 isaligned with a beach 210 and each influent inlet port 206 is locatedbetween adjacent pairs of beaches 210 (FIG. 16). Since treatment cells610 are hydraulically connected, from approximately the mid-depth pointof reservoir 104 to bottom floor 110, any fluid removed from the middleor lower portions of clarifier 10 flows continuously from all cells 610(this is true for both effluent and bottom recycle).

FIGS. 17-19 shows the rotating subassemblies of FIG. 16 superimposed onthe fixed trough subassembly of FIG. 15 to further illustrate the timedporting features of the invention (as explained above, although ports138, 206, 208 and 312 are shown in concentric arrangement for thepurposes of clarity, at least some of the ports may in fact besuperimposed one above the other). Referring to FIG. 17 and liquidtreatment cell 610 labeled “A” (i.e. 610A), a leading edge 213 of abeach 210 is aligned with the front edge 314 of trough 306. Thus beach210 is about to begin sliding underneath a corresponding trough 306. Intreatment cell 610A, movable inlet port 206 is in full register withfixed feed port 138 to enable full flow of influent from influent supplychamber 132 into reservoir 104 between rear edge 316 of trough 306 andthe next-in-sequence beach 210.

Baffles 220, 222 direct the flow of influent introduced into eachtreatment cell 610. In particular, influent flows into cell 610 througha feed port 138 and is directed radially outwardly by skewed baffles222. The canted mid-radius baffle 220 deflects the majority of thefloating solids (or other separable matter) toward the surface ofreservoir 104 to form a float blanket of flocculent. Some solids willsettle between skewed baffles 222 and be removed from clarifier 10 viabottom rakes 226 as described above. In the region of the skewed radialbaffle tie bars 223, which connect baffles 222 together, there is agentle downward flow created by the upward flow between the adjacentbaffles (FIG. 6).

Further, the closed portion between baffles 222 (denoted by numerals 1and 2 in FIG. 16) defines a portion of each treatment cell 610 wherefluid down-flow is allowed to occur in response to the fluid up-flow inthe open portions between baffles 222 which are in direct communicationwith an open feed port 138 (such open portions are denoted by numerals 3and 4, for example, in FIG. 16). This provides energy dissipation in anup-flow/down-flow manner around the intervening baffle 222 between theclosed and open portions. The upflow in regions 3 and 4 in the vicinityof feed port 138 (FIGS. 16 and 17) is caused by the release of largebubbles contained in the influent liquid. As mentioned above, thepresence of the upwardly directed mid-radius baffles 220 at the outerend of the skewed baffles 222 also contributes to up-flow in thisregion. In one embodiment, the horizontal inlet velocity of influentshould be on the order of 10-15 feet per minute for good flocculationand flow distribution. In the case of the present invention, thehorizontal inlet velocity may be advantageously reduced due to thepresence of the vertical flow vector discussed above which helpsdissipate the fluid energy.

Referring to treatment cell 610B of FIG. 17, an inlet port 206 is inpartial alignment with a corresponding feed port 138 to permit partialintroduction of influent into treatment cell 610B between the rear edge316 of a trough 306 and the trailing edge 214 of a downstream beach 210and scraper blade 408. In treatment cell 610B rotation of supportcylinder 202 is causing increased opening of the feed port 138 alignedwith that cell (i.e. port 206 is coming increasingly in register withport 138).

Referring next to treatment cell 610C, no inlet port 206 is in completeor partial register with a corresponding feed port 138. Accordingly, awall portion of rotating cylinder 202 completely obstructs the feed port138 in alignment with cell 610C to prevent introduction of influentthereinto. Accordingly treatment cell 610C is relatively quiescent topermit optimum flotation of flocculent as described further below.

Referring next to treatment cell 610D, here again no inlet port 206 isin complete or partial register with a corresponding feed port 138 andhence no influent is being introduced into cell 610D. In cell 610D beach210 has moved directly underneath trough 306 and scraper 408 has beenbrought into alignment with front edge 314 of trough 306. Accordingly,in cell 610D movement of scraper blade 408 is causing flocculent togently spill into trough 306. At the same time, a movable flocculentoutlet port 208 has been brought into partial alignment with aflocculent discharge port 312 to allow discharge of flocculent fromtrough 306 into holding tank 124 as described above.

Finally, referring to treatment cell 610E, an inlet port 206 is inpartial register with a corresponding feed port 138 to permitintroduction of influent into cell 610E between the rear edge 316 of atrough 306 and the trailing end 214 of a downstream beach and scraperblade 408. Thus cell 610E is in a similar operational state to that ofcell 610B. However, in cell 610E continued clockwise rotation of supportcylinder 202 is causing increased closure rather than increased openingof the corresponding feed port 138.

Thus it can be seen from FIG. 17 that, due to the timed porting featureof the invention, cells 610A-610E are simultaneously in differentoperational states although influent is being introduced into reservoir104 continuously from influent supply chamber 132. More particularly,one of the cells 610 (cell A) is fully filling, two cells 610 (cells Band E) are partially filling and two cells (cells C and D) are notfilling. At the selected time only one of the troughs 306 (in cell D) isdischarging flocculent through aligned ports 208, 312 into a flocculentcollection conduit 154 and hence into holding tank 124.

FIG. 18 shows the configuration of FIG. 17 later in time with lower andupper rotating subassemblies 200, 400 (and hence beaches 210 and scraperblades 408) rotated clockwise a further 9° relative to stationarytroughs 306. Referring to treatment cell 610A, at this selected timebeach 210 is beginning to pass underneath a corresponding trough 306 andscraper blade 408 is approaching the front edge 314 of trough 306.Flocculent in advance of scraper blade 408 is beginning to spill intotrough 306 and a flocculent outlet port 208 is beginning to come intoalignment with a discharge port 312, thus enabling passage of flocculentfrom trough 306 into a flocculent collection conduit 154 and holdingtank 124. Influent continues to be introduced into treatment cell 610Abetween the rear edge 316 of trough 306 and the next-in-sequence beach210, but feed port 138 aligned with cell 610A is beginning to close(i.e. inlet port 206 and feed port 138 are now only in partialalignment).

At the selected time shown in FIG. 18, trough 306 is disposedapproximately mid-way between the two scraper blades 408 definingtreatment cell 610B. An influent inlet port 206 is almost in fullalignment with a corresponding feed port 138 and influent is continuingto be introduced into cell 610B in a fill subzone 612 defined betweenthe rear edge 316 of trough 306 and the next-in-sequence scraper blade408 and beach 210.

Referring now to cell 610C, at the selected time shown in FIG. 18 aninlet port 206 is beginning to be brought into alignment with acorresponding feed port 138 and hence influent is now beginning to beintroduced downstream of the trough rear edge 316. Upstream (i.e.counterclockwise) from the trough front edge 314 the mixed liquor orother liquid to be clarified is continuing to be maintained in asubstantially quiescent state.

Referring next to cell 610D at the selected time shown in FIG. 18, noinlet port 206 is in alignment with a corresponding feed port 138 andhence feed port 138 in cell 610D remains closed. As a result, noinfluent is being introduced directly into cell 610D and the mixedliquor therein is therefore substantially quiescent. The leading edge213 of beach 210 has now advanced beyond the rear edge 316 of trough306. Scraper blade 408, located at the trailing edge 214 of beach 210,has traversed mid-way across trough 306 at an elevated position abovetrough 306. By this time outlet port 208 has moved out of register withdischarge port 312 aligned with cell 610D and hence port 312 is closed,thereby preventing discharge of any further flocculent from cell 610Dinto holding tank 124.

Referring lastly to cell 610E at the selected time shown in FIG. 18,inlet port 206 is continuing to move further out of alignment with acorresponding feed port 138. However, feed port 138 remains open a smallamount to permit continued introduction of influent into treatment cell610E at a location between the rear edge 316 of trough 306 andnext-in-sequence beach 210 and scraper blade 408.

FIG. 19 shows the configuration of FIG. 18 later in time with lower andupper rotating subassemblies 200, 400 (and hence beaches 210 and scraperblades 408) rotated clockwise a further 9° relative to stationarytroughs 306 (i.e. rotated a total of 18° relative to the configurationof FIG. 17). Referring to treatment cell 610A, at this selected timebeach 210 has now passed fully underneath trough 306 and hence beach 210and trough 306 are in full alignment. Scraper blade 408 is being liftedvertically along the front edge 314 of trough 306 as described above andflocculent in advance of scraper blade 408 is continuing to spill intotrough 306. Flocculent outlet port 208 continues to be in partialalignment with discharge port 312, permitting continued discharge offlocculent into holding tank 214 (as shown by an arrow in FIG. 19). Atthis point in time cell 610A is the only treatment cell 610 from whichflocculent is being discharged. Influent continues to be introduced intotreatment cell 610A between the rear edge 316 of trough 306 and thenext-in-sequence beach 210 and scraper blade 408 but feed port 138 iscontinuing to close (i.e. inlet port 206 is now in a lesser degree ofalignment with feed port 138 as compared to the configurations of FIGS.17 and 18).

Referring now to treatment cell 610B, at the selected time shown in FIG.19 the leading edge 213 of beach 210 is now aligned with the front edge314 of trough 306. Additionally inlet port 206 is now in full alignmentwith a corresponding feed port 138. Accordingly, influent is beingintroduced into treatment cell 610B at a maximum rate.

Referring next to treatment cell 610C, at the selected time shown inFIG. 19, an inlet port 206 is in partial alignment with a feed port 138and influent is being introduced between the rear edge 316 of trough 306and the downstream (i.e. clockwise direction) scraper 408. However, noinfluent is being introduced into treatment cell 610C upstream of trough306 (i.e. in a counterclockwise direction).

Referring next to treatment cell 610D at the selected time shown in FIG.19, scraper blade 408 has now traversed across the entire width oftrough 306 at an elevation above trough 306. Scraper blade 408 thendescends at the rear edge 316 of trough 306 back into contact with orproximate to beach 210. Inlet ports 206 and feed ports 138 continue tobe misaligned and hence no influent is flowing into treatment cell 610D.

Referring lastly to cell 610E at the selected time shown in FIG. 19,inlet port 206 has moved entirely out of alignment with thecorresponding feed port 138 and hence feed port 138 is now fully closed.The mixed liquor or other liquid to be clarified resident within cell610E is therefore relatively quiescent to facilitate flotation offlocculent therein.

As should be apparent from FIGS. 17-19 in view of the above description,each cell 610 may be in one of several operational states at anyselected time depending upon the relative position of a beach 210,scraper blade 408 and trough 306. For example, cell 610 is in a “fill”operational state when a feed port 138 in communication with cell 610 isfully open (i.e. feed port 138 and inlet port 206 are fully aligned) andthe entire available treatment area of cell 610 is receiving influent.By way of illustration, cell 610A in FIG. 17 is in a “fill” state.

By contrast, cell 610 is in a “float” operational state when feed port138 is fully closed (i.e. feed port 138 is not in alignment with aninlet port 206) and hence no influent is being introduced into cell 610.In the “float” operational state the entire available treatment area ofcell 610 is relatively quiescent and undisturbed to optimize flotationof flocculent. By way of illustration, cell 610D in FIG. 17 is in a“float” state.

Further, cell 610 is in a “fill/float” operational state when a fillsubzone 612 of cell 610 is filling while another separate float subzone614 of cell 610 is floating. In this case a feed port 138 is in onlypartial alignment with an inlet port 206 and only the fill subzone 612is receiving a supply of influent. By way of illustration, cell 610B inFIG. 17 is in a “fill/float” operational state. In particular, the fillsubzone 612 between the rear edge 316 of trough 306 and thenext-in-sequence beach 210 and scraper blade 408 is filling withinfluent and the float subzone 614 between the front edge 314 of trough306 and the previous-in-sequence scraper blade 408 is quiescent and isnot receiving any influent. As the two scraper blades 408 defining acell 610 continue to rotate relative to a stationary trough 306, thefill subzone 612 becomes relatively larger and the float subzone 614becomes relatively smaller (although the treatment cells 610 arehydraulically connected as described above, the surface area between aselected trough 306 and scraper blade 408 changes as assembly 406rotates within clarifier bowl 102). For example, referring again to cell610B in FIG. 17, the fill subzone 612 covers a segment 18° in size andthe float subzone 614 covers a segment 36° in size (including theportion above beach 210). Referring to FIG. 18, when beaches 210 andscraper blades 408 have rotated a further 9°, both the fill subzone 612and the float subzone 614 of cell 610B cover a segment 27° in size.Referring now to FIG. 19, when beaches 210 and scraper blades 408 haverotated a further 9° the fill subzone 612 of cell 610B covers a segment36° in size and the float subzone 614 of cell 610B covers a segment 18°in size (i.e. only the portion above beach 210). As indicated above,depending upon the time in the cycle, one of the float subzone 614 orthe fill subzone 612 may be reduced to zero and the other subzone may beat its maximum size.

As beach 210 rotates through a treatment region 600 of clarifier 10between troughs 306 (FIG. 15), it creates a shear plane below the levelof the flocculent blanket forming on the surface of the liquid. When theleading edge 213 of the beach 210 reaches the front edge 314 of the nexttrough 306 in the direction of rotation (see, for example treatment cell610A of FIG. 17 or treatment cell 610B of FIG. 19), it forms the bottomboundary of the float subzone 614. The floating flocculent is thereforeconfined within the float subzone 614 (i.e. bounded by beach 210,scraper blade 408, front edge 314 of trough 306, rotating cylinder 202and outer baffle 304). At this point in the cycle the float subzone 614is confined above beach 210 and is not hydraulically connected to thefill subzone 612.

As beach 210 and scraper blade 408 continue to rotate, the volume of thefloat subzone 614 decreases progressively which causes the liquidconfined within the float subzone 614 to rise. In particular, the floatblanket on the surface of the liquid confined within the float subzone414 rises in a manner analogous to a ship rising in a water lock to anelevation above the fill level of the remainder of the liquid containedwithin reservoir 104. As scraper blade 408 continues to rotate, thefloat blanket of flocculent is lifted to a height sufficient for it togently spill over front edge 314 into trough 306. This feature of theinvention minimizes disruption of fragile flocculent.

Shortly after the leading edge 213 of beach 210 moves into alignmentwith the front edge 314 of the next trough 306 in the direction ofrotation, a “draw” operational state begins wherein flocculent from thefloat subzone 614, which spills into trough 306 as discussed above, isdrawn through discharge port 312 into a collection conduit 154 and henceinto holding tank 124. By way of illustration, cell 610A in FIG. 17 isabout to begin the draw state and cell 610E has just finished the drawstate. During the draw state flocculent outlet port 208 and flocculentdischarge port 312 are brought into at least partial alignment (i.e.port 312 is open). The draw state begins when port 312 opens andcontinues for approximately 18° of rotation of lower and upper rotatingsubassemblies 200, 400 during which time scraper blade 408 contacts andtraverses up front edge 314 of trough 306 to a position above trough 306as described above. During the draw state the fill subzone 612 of thetreatment cell 610 (i.e. downstream or in a clockwise direction from therear edge 316 of trough 306) can continue to receive influent whilescraper blade 408 traverses over trough 306.

When scraper blade 408 reaches the rear edge 316 of trough 306 itdescends rapidly downwardly as described above on or proximate to beach210 near the trailing edge 214 thereof (in the case of the “full bite”adjustment of FIG. 8( c)). This marks the end of the draw state for thetreatment cell 610 in question.

As will be appreciated by a person skilled in the art, each treatmentcells 610 cycles through the above described fill, float and drawoperational states as lower and upper rotating subassemblies 200, 400rotate relative to fixed subassemblies 100, 300 and 500. With referenceto the illustrated embodiment of FIGS. 17-19, at each 18° interval onefeed port 138 aligned with one treatment cell 610 is fully open, twofeed ports 138 aligned with two different treatment cells 610 arepartially open (one port 138 is opening and one closing), and two feedports 138 aligned with the remaining two treatment cells 610 are fullyclosed. By way of example, comparing FIGS. 17 and 19, the operationalstate of cell 610A shown in FIG. 17 is the same as the operational stateof cell 610B shown in FIG. 19; the operational state of cell 610B shownin FIG. 17 is the same as the operational state of cell 610C shown inFIG. 19; the operational state of cell 610C shown in FIG. 17 is the sameas the operational state of cell 610D shown in FIG. 19; the operationalstate of cell 610D shown in FIG. 17 is the same as the operational stateof cell 610E shown in FIG. 19; and the operational state of cell 610Eshown in FIG. 17 is the same as the operational state of cell 610A shownin FIG. 19.

The timed porting feature of the invention, including the fill, float,and draw sequences, is further illustrated with reference to Table 1below. Table 1 illustrates the operational state of each of fivetreatment cells 610 (i.e. A, B, C, D and E) as subassemblies 200, 400,including beaches 210 and scrapers 408, rotate within clarifier bowl 102in successive 18° intervals. Although FIGS. 17 and 19 illustrate onlythe first 18° rotational interval, it will be appreciated by a personskilled in the art that rotation of the various rotating clarifiercomponents would continue in the same manner. The left column of Table 1records the clockwise degrees of rotation (e.g. of beaches 210 andscraper blades 408) and the top row describes the position of the feedports 138 aligned with each selected cell 610 (except in the case of thedraw state where opening of flocculent discharge port 312 is referredto). Information is recorded in Table 1 for each of the five treatmentcells 610A-E at each 18° interval of rotation.

TABLE 1 Float/Dwell/Draw Fill 0° 18° 36° 54° 72° 90° 108° 126° 144°Scraper and Beach Rotation ↓ Fill Cycle Float Cycle (clockwise) (Back ofScraper) (Front of Scraper) FC = full closed Duration 72° Duration 54°Draw ½C = half closed Port Port Port Port Port Port Port Duration 18° FO= full open FC → ½O; ½O → FO; FO → ½C ½C → FC FC → FC FC → FC FC → FCPort ½O = half open begin fill cont. fill cont. fill end fill beginfloat cont. float end float FC → FO Drawing location {circle around (1)}{circle around (2)} {circle around (3)} {circle around (4)} {circlearound (5)} {circle around (6)} {circle around (7)} {circle around (8)}0°-18° C B A E D C B A 18°-36° D C B A E D C B 36°-54° E D C B A E D C54°-72° A E D C B A E D 72°-90° B A E D C B A E 90°-108° C B A E D C B A. . . . . . . . . . . . . . . . . . . . . . . . . . . 162°-180° B A E DC B A E Repeat cycle for: 180°-270° 270°-360°

As discussed above, each treatment cell 610 is arbitrarily definedbetween a pair of spaced-apart scraper blades 408, namely a leadingscraper blade 408 traveling in the direction of rotation and a trailingscraper blade 408 traveling behind the leading blade in the samedirection of rotation. Due to this spaced radial arrangement, a leadingscraper blade 408 defining the leading boundary of one selectedtreatment cell 610 is also the trailing scraper blade 408 of theimmediately down-stream (i.e. clockwise direction) treatment cell 610.Conversely the trailing scraper blade 408 defining the trailing boundaryof a selected treatment cell 610 is the leading scraper blade 408 of theimmediately upstream (counterclockwise direction) treatment cell 610.Thus the position of each cell 610 is changing with time as the scraperblades 408 rotate as described above. Each cell 610 is thereforesequentially brought into alignment with different feed ports 138 whichare fixed in position on central hub 106 (FIG. 5). As described above,feed ports 138 may either be fully open, partially open and partiallyclosed, or fully closed depending upon whether they are fully orpartially aligned with one of the rotating inlet ports 206 formed onrotating cylinder 202. In the illustrated embodiment (FIGS. 2 and 3),clarifier 10 includes four fixed feed ports 138 and five rotating in letports 206. Accordingly, for each complete rotation of cylinder 202, eachfeed port 138 is fully open 5 times.

As will be appreciated by a person skilled in the art, the port timingmechanism illustrated in FIGS. 17-19 and Table 1 and described above isfor illustrative purposes only. The number, size, shape and location ofports 138, 206, 208 and 312 may vary according to the process designrequirements of clarifier 10. For example, the exact size and locationof the ports may be optimized to satisfy the process requirements of aspecific application using computational fluid dynamics analyses and thelike.

In the example shown in FIGS. 17-19 and Table 1, if a particulartreatment cell 610 straddles a fixed trough 306, cell 610 is subdividedinto a fill subzone 612 between trough 306 and the leading scraper 408and a float subzone 614 between the same fixed trough 306 and thetrailing scraper 408 (see, for example, cell 610B in FIG. 17). The inletports 206 are aligned so that only the fill subzone 612 of cell 610B isin communication with an open feed port 138 to permit influent inflow.The float subzone 614 does not directly receive a supply of influent andtherefore remains relatively undisturbed. In other words, during theperiod that a trailing scraper blade 408 is positioned on acorresponding beach 210 spaced-apart from a trough 306, the areaclockwise from the scraper blade 408 to the next-in-sequence trough 306is available for flotation whereas the area counter-clockwise from thescraper blade 408 (i.e. in the next-in-sequence treatment cell 610) isavailable for filling.

As the scraper blades 408 rotate, the leading scraper blade 408 willcontinue to move away from a fixed trough 306 and hence the fill subzone612 will expand in size as described above. Conversely, as the trailingscraper blade 408 moves toward a fixed trough 306 the float subzone 614will become progressively smaller. Eventually the beach 210 disposedbelow the trailing scraper blade 408 will reach the front edge 314 of atrough 306 (for example, as shown in cell 610A in FIG. 17). At thispoint beach 210 forms the bottom boundary of the float subzone 614 asdescribed above. As cylinders 202 and 402 continue to rotate, beach 210will begin to slide underneath trough 306 (see cell 610A in FIG. 18) andthe flocculent from the float subzone 614 will spill into trough 306 andbe discharged through flocculent discharge port 312 as described above.When the trailing scraper blade 408 reaches the front edge 314 of trough306, the float subzone 614 has in effect been reduced to zero and thefill subzone 612 of the treatment cell 610 has increased to its maximumsize (54° in this example as shown in 610A of FIG. 19).

The trailing scraper 408 then traverses over trough 306 as describedabove and descends at the rear edge 316 of trough 306 back on orproximate to beach 210 (see, for example, cell 610D of FIG. 17). At thisstage the cell 610 does not straddle a trough 306 (i.e. the leadingscraper blade 408 is aligned with the front edge 314 of one trough 306and the trailing scraper blade 408 is aligned with the rear edge 316 ofanother trough 306). Accordingly, at this stage the cell 610 is notsubdivided into a separate fill subzone 612 and float subzone 614.Rather the entire cell 610 constitutes a float subzone 614 of maximumsize. Continued rotation of the scraper blades 408 causes the leadingscraper blade 408 to move away from the trough 306 until cell 610straddles a trough 306 and the cell 610 is therefore once againsubdivided into a separate fill subzone 612 receiving influent and afloat subzone 614 not directly receiving influent. The inlet ports 206are configured to begin opening a feed port 138 to permit passage ofinfluent into the fill subzone 612 as soon as the leading scraper blade408 passes the rear edge 316 of a trough 306). For example, referring toFIG. 18 and cell 610C, when the leading scraper blade 408 moves awayfrom trough rear edge 316, influent begins to flow into fill subzone 612between scraper blade 408 and trough 306.

Referring again to Table 1, the fill cycle occurs behind the directionof rotation of the leading scraper blade 408 (i.e. between the leadingscraper blade 408 and an upstream trough 306) whereas the float cycleoccurs in advance of the trailing scraper blade 408 (i.e. between thetrailing scraper blade 408 and a downstream trough 306). The draw state,during which time the flocculent is spilled into a trough 306 anddischarged therefrom through ports 312, occurs toward the end of thefloat cycle in advance of the trailing scraper blade 408.

The timed porting features of the invention summarized in Table 1 may befurther illustrated by considering a specific treatment cell 610, namelytreatment cell 610C of FIGS. 17-19. At an arbitrary initial time theleading boundary (i.e. leading scraper blade 408) of cell 610C has justpassed over a trough 306 and is aligned with the rear edge 316 of thetrough 306. The fill cycle is therefore about to begin. At this pointcell 610C is not in communication with an open feed port 138 and theentire flocculent contents of the cell 610C are floating relativelyundisturbed. Rotation of cell 610C from 0° to 18° (i.e. due to rotationof lower and upper subassemblies 200, 400 relative to fixedsubassemblies 100, 300 and 500) causes cell 610C to become subdividedinto separate fill and float subzones 612, 614 (FIG. 19). In particular,fill subzone 612 is brought into communication with a feed part 138which has been adjusted from a fully closed to a half open configurationas the feed port 138 becomes aligned with an inlet port 206. Meanwhile,a different feed port 138 aligned with float subzone 614 remains closedand hence flocculent in this subzone 614 continues to float relativelyundisturbed. The timed porting feature of the invention thereforeessentially permits batch flotation of the mixed liquor or otherinfluent (i.e. in the relatively undisturbed float subzones 614) eventhough the overall infeed/outfeed process is continuous.

Continued rotation of cell 610C from 18° to 36° as shown in Table 1causes the feed port 138 aligned with fill subzone 612 to be adjustedfrom a half open to a fully open position (i.e. this feed port 138 isnow fully aligned with an inlet port 206). The feed port 138 alignedwith float subzone 614 remains fully closed. As the treatment cell 610Crotates, the fill subzone 612 is becoming progressively larger and thefloat subzone 614 is becoming progressively smaller.

Continued rotation of cell 610C from 36° to 54° as shown in Table 1causes the feed port 138 aligned with fill subzone 612 to be adjustedfrom a fully open to a half closed position (i.e. this feed port 138 isnow only partially aligned with an inlet port 206). The fill subzone 612continues to become progressively larger in size. At the same time thefloat subzone 614 is reducing in size to zero as the float cycle endsand the floated flocculent spills over into a trough 306 and isdischarged through a discharge port 312 and collection conduit 154 intoholding tank 124. Accordingly two separate functions, namely filling anddrawing are occurring within cell 610C simultaneously at differentlocations. This “feed port overlap” feature enhances the flotationcapacity of clarifier 10. By the end of this segment of rotation thetrailing scraper blade 408 is aligned with the front edge 314 of atrough 306.

Continued rotation of cell 610C from 54° to 72° as shown in Table 1causes the feed port 138 aligned with fill subzone 612 to be adjustedfrom a half closed to a fully closed position (i.e. this feed port 138is now fully obstructed by a wall portion of cylinder 202). The fillsubzone 612 has now achieved its maximum size, the fill cycle for thistreatment cell 610C has ended and a float cycle is about to begin. Atthe same time the trailing scraper blade 408 has lifted off of itscorresponding beach 210 and is traversing above a trough 306 asdescribed above.

Continued rotation of cell 610C from 72° to 90° causes the trailingscraper blade 408 to rotate away from the rear edge 316 of a trough 306while the leading scraper blade traverses over the next-in-sequencetrough 306 as described above. During this period cell 610C is inalignment with a single feed port 138 that remains fully closed.

The above described fill, float draw cycle is then repeated for rotationof cell 610C between further rotation intervals, namely 90° to 180°,180° to 270° and 270° to 360°. Accordingly, in this example, one full360° rotation of rotating subassemblies 200, 400 relative to fixedsubassemblies 100, 300 and 500 causes treatment cell 610 to spill itsshare of floated flocculent four separate times into four separatetroughs 306. Meanwhile the same operational cycles are ongoing in theother cells 610 in a staggered time sequence as shown in Table 1. Forexample, with reference to Table 1, it is apparent that treatment cell610A is in the same operational state during interval 0° to 18° astreatment cell 610C is during interval 36° to 54°. Accordingly, in thisexample, at any selected time only one of the five treatment cells 610is in the draw state discharging flocculent (the port referred to in thedraw state shown in the final column of Table 1 is the flocculentdischarge port 312). This ensures that the discharge load isintermittent and achieves differential loading on the clarifier drivemeans.

Numerals 1-8 in Table 1 denote the locations identified in FIGS. 17-19.The left column of Table 1 represents a dynamic record of thefill-float-draw operational states (i.e. as each cell 610 rotates insequence) while the rows of the table provide the same information understatic conditions. The dynamic operation of a single cell 610 rotatingclockwise 18° at a time can also be fully described by looking at thestatic representation shown in, for example, FIG. 17 and readingcounterclockwise one cell 610 at a time. In other words, in is example,as the mechanical rotation of a scraper blade 408 moves clockwisethrough a full cell segment of 72°, the sequence of opening of ports 138moves counterclockwise (through 5 cell widths or 360 degrees).

In summary, as exhibited by Table 1 and the above-described example, assoon as a scraper blade 408 descends at the rear edge 316 of any onetrough 306, the first cell 610 located clockwise from the trough 306begins a float cycle for 54° of rotation while the cell 610 locatedcounter-clockwise from the first cell 610 begins a fill cycle for 72° ofrotation (as explained above filling may occur within a treatment cell610 during the drawing state). That is, in any pair of adjacent cells610, the clockwise cell 610 is in the float portion of the cycle whilesimultaneously the counter-clockwise cell 610 is in the fill portion ofthe cycle in this example. Shortly after the leading edge 213 of beach210 in any cell 610 reaches the front edge 314 of a trough 306 in thatcell 610, the float cycle notionally ends and the draw cycle begins forapproximately 18° rotation during which the flocculent collected in thefloat subzone 614 is gently spilled into the trough 306 and dischargedinto the holding tank 124. During the draw cycle the flocculentdischarge port 312 aligned with the trough 306 in question opens.

When a beach 210 is passing under a trough 306 there is a “dwell” periodof sufficient length for the upper rotating assembly 400 to traverseslightly more than 18°. This dwell period allows the scraper blade 408to traverse over the trough 306 and rapidly descend on to itscorresponding beach 210 as described above. The draw operational statemay occur during a portion of the dwell period. For example, aflocculent discharge port 312 may be open during the initial portion ofthe dwell period as the trailing scraper blade 408 is lifted vertically.Port 312 then closes. One benefit of the means described herein tovertically displace the scraper blade 408 is that the blade 408 islifted clear of the beach 210 above trough 306 for the shortest possibledwell period. In other words, each scraper blade 408 traversessubstantially all of the available surface area of the treatment regions600 defined between the troughs 306. Since the dwell period isminimized, the length of time available for filling and flotation ismaximized, thereby optimizing the efficiency of clarifier 10. Inalternative embodiments of the invention the length of the float cyclecould be lengthened and the length of the fill cycle could becorresponding shortened. However, in the example shown in FIGS. 17-19,the combined length of the fill-float-draw periods does not exceed 144°of rotation for any pair of adjacent cells 610.

Operation

In operation, clarifier 10 is initially connected to an influent source,such as an upstream vertical shaft bioreactor providing a continuoussupply of mixed liquor. As described above, the mixed liquor may bedelivered to an influent supply chamber 132 located within a central hub106 of clarifier 10 through supply lines 150, 152 (FIG. 5). The influentmixture is controllably introduced into clarifier reservoir 104 fromsupply chamber 132 through feed ports 138 in a timed sequence. Asdescribed above, feed ports 138 are periodically brought into alignmentwith inlet ports 206 formed on a cylinder 202 rotating around hub 106.The influent is initially supplied to reservoir 104 to a fill levelapproximating the elevation of flocculent collection troughs 306 whichextend radially at spaced locations within the clarifier bowl 102.

Suspended solids (or other separable matter) present in the mixed liquorinfluent are caused to rise in reservoir 104, such as by a gas flotationprocess, to form a surface layer of flocculent. A plurality of rotatingbeaches 210 and scraper blades 408 are provided as described in detailabove for handling the flocculent. Rotation of both beaches 210 andblades 408 is actuated by a common drive 502.

Rotation of beaches 210, baffles 220, 222 and scraper blades 408functionally subdivides reservoir 104 into a plurality of separateinfluent treatment cells 610. Each cell 610 is further subdividable intoa fill subzone 612 receiving influent infeed through ports 138 and afloat subzone 614 which does not directly receive influent infeed and istherefore relatively quiescent. Rotation of beaches 210 and scraperblades 408 relative to troughs 306 causes the fill subzones 612 toprogressively increase in size and the float subzones 614 toprogressively decrease in size as described above. The floatingflocculent within the float subzones 614 is thereby caused to gentlyspill into the flocculent collection troughs 306 in a timed sequence. Ahead difference is maintained between the flocculent collection troughs306 and holding tank 124 within central hub 106 so that flocculent flowsintermittently from troughs 306 into tank 124 without the use of pumps.The flocculent may comprise, for example, return activated sludge whichis then recirculated through recycle line 160 to an upstream aerator,bioreactor or other processor. A non-recyclable fraction of theflocculent, such as waste activated sludge, is separately dischargedfrom troughs 306 into discharge lines 132 (FIG. 5).

In an alternative embodiment of the invention illustrated in asimplified, schematic form in FIG. 20 the recycle flow from reservoir104 may be regulated in treatment cells 610 undergoing flotation. Thisfeature may be particularly desirable in applications having a highrecycle rate, such as biological nutrient removal applications.According to the embodiment, rotation of shutter ring 240 (FIG. 6)causes shutters 242 to periodically come into alignment with standpipeinlet ports 170 (FIG. 5). For example, depending upon the specificlocation of inlet ports 170 in sump 128, ports 170 could become openedwhen a shutter 242 extends thereover or passes thereunder. The primarypurpose of this feature is to ensure that recycling of bottom solidsdoes not occur in treatment cell(s) 610 undergoing flotation, therebymaintaining the mixed liquor in such treatment cell(s) in a relativelyquiescent state. For example, in FIG. 20, only cells 610A and 610E aredischarging bottom recycle from a lower portion thereof. In the othertreatment cells 610 shutter 242 is not aligned with an inlet port 170.Other equivalent means for limiting solids recycle in treatment cells610 undergoing flotation may be envisioned by a person skilled in theart.

As indicated above, influent is introduced into clarifier reservoir 104continuously. Clarified effluent is also removed from clarifier 10continuously from a perimeter weir 114 through effluent dischargeconduit 122 (FIG. 5). The internal recycle stream described above helpsbalance varying influent and effluent flows and maintains the headdifference between reservoir 104 and holding tank 124.

The scraper blades 408 traverse substantially all of the effectivesurface area of clarifier reservoir 104 between troughs 306. Each blade408 is vertically displaced above its corresponding beach 210 when theblade 408 traverses past a trough 306 as described in detail above.

As will be apparent from the foregoing, clarifier 10 has severalimportant operational advantages, including the following:

-   1. Although influent is introduced into clarifier 10 continuously,    flocculent is permitted to float undisturbed in relatively quiescent    float subzones 614 in a batch-like fashion.-   2. Since mechanical handling of the float blanket is minimized, the    clarifier 10 is particularly well suited to handling of fragile    flocculent without the need to use polymers.-   3. Due to the feed port overlap feature, both influent infeed and    flotation, or influent infeed and drawing of flocculent from    flocculent discharge troughs 306, may occur simultaneously in    different subzones of the same treatment cell 610, thereby    maximizing flotation efficiency.-   4. The influent is introduced into a fill subzone which is expanding    in size.-   5. The discharge of flocculent into the flocculent collection    troughs 306 is timed to stagger the intermittent load.-   6. Flocculent can be discharged from the collection troughs 306 into    the holding tank 124 for recycle without the use of pumps.-   7. All of the rotating elements of the clarifier may be driven by a    single drive means.-   8. The scraper lifting mechanism converts radial horizontal movement    to vertical movement. In particular, rotating movement of the    scraper blade 408 along a radial line is temporarily halted while    the scraper blade is displaced vertically along the front edge 314    of a flocculent collection trough 306. Rotating movement of blade    408 then resumes to enable blade 408 to traverse over trough 306 and    descend on to or proximate an underlying beach 210. This feature    ensures that the scraper blade 408 will traverse substantially all    of the available surface area of the clarifier reservoir 104 between    the flocculent collection troughs 306. Further, the scraper lifting    functionality is achieved using a minimal number of mechanical parts    and does not interfere with the operation of other flocculent    handling assemblies 406 which continue to rotate within clarifier 10    at a constant velocity.-   9. The circular design maximizes the effective length of the beaches    210. Since the beaches 210 are submerged and horizontally oriented,    they provide shear planes beneath the surface float blanket.-   10. The clarifier capacity can be adjusted by altering the landing    spot of a scraper blade 408 on or proximate to a corresponding beach    210.

As will be apparent to those skilled in the art in the light of theforegoing disclosure, many alterations and modifications are possible inthe practice of this invention without departing from the spirit orscope thereof. Accordingly, the scope of the invention is to beconstrued in accordance with the substance defined by the followingclaims.

1. A method of treating liquid influent in a circular clarifier having acontainer for holding said influent and at least one trough extending atapproximately the fill level of said influent within said container,said method comprising: (a) introducing said influent into a treatmentregion of said container in the vicinity of said trough; (b) causing afraction of said influent comprising separable matter to form a surfacelayer of flocculent in a flotation subzone of said treatment region; and(c) confining said flocculent within said flotation subzone andgradually decreasing the volume of said flotation subzone to cause saidflocculent to rise above said fill level and gently spill into saidtrough without substantially disrupting said flocculent, wherein saidclarifier comprises a rotatable flocculent handling assembly and whereinsaid step of gradually decreasing the volume of said flotation subzonecomprises rotating said flocculent handling assembly through saidtreatment region, and wherein said flocculent handling assemblycomprises a beach having a generally horizontally disposed uppersurface, wherein said beach defines the lower boundary of said flotationsubzone.
 2. The method as defined in claim 1, wherein rotation of saidflocculent handling assembly in said treatment region increases theconcentration of said flocculent in said flotation subzone.
 3. Themethod as defined in claim 2, wherein said flocculent handling assemblyfurther comprises a scraper blade extending upwardly from said beach. 4.The method as defined in claim 1, wherein said separable matter iscaused to form said surface layer of flocculent by a gas flotationprocess and wherein treatment region is operable in a fill phase, afloat phase or a combination fill/float phase.
 5. The method as definedin claim 4, wherein rotation of said flocculent handling assemblythrough said treatment region subdivides said region into said flotationsubzone in advance of the direction of travel of said assembly and afill subzone behind said assembly, wherein said influent is introducedinto said fill subzone of said treatment region in said fill phase andsaid fill/float phase.
 6. The method as defined in claim 1, wherein saidtrough is stationary and said flocculent handling assembly is movablerelative to said trough.
 7. The method as defined in claim 1, whereinsaid beach forms a fluid shear plane within said treatment regionproximate a lower portion of said flocculent.
 8. The method as definedin claim 1, wherein said influent is introduced into said containercontinuously.
 9. The method as defined in claim 3, wherein said influentis introduced into said container continuously.
 10. The method asdefined in claim 9, wherein said clarifier comprises a plurality ofradially-spaced apart troughs and a plurality of separate treatmentregions, each of said treatment regions being defined between anadjacent pair of said troughs, wherein said influent is sequentiallyintroduced into said treatment regions in a timed sequence such thatsaid flocculent is substantially quiescent in at least some of saidflotation subzones in advance of the direction of rotation of saidflocculent handling assembly.
 11. The method as defined in claim 10,wherein said scraper blade traverses substantially all of the exposedsurface of said treatment regions as it rotates within said container.12. The method as defined in claim 11, further comprising verticallydisplacing said scraper blade in the vicinity of each of said troughs toenable said scraper blade to pass thereover and then descend into thenext-in-sequence one of said treatment regions.
 13. The method asdefined in claim 12, wherein said container is defined between a centralhub and a peripheral wall of said clarifier, and wherein each of saidtroughs extends radially within said container at spaced locations, saidcentral hub having a plurality of feed ports formed therein at spacedlocations, wherein the step of introducing influent into said treatmentregions in a timed sequence comprises rotating a first rotatable ringaround said hub, said ring having a plurality of influent inlet portswhich are sequentially brought into at least partial register with saidfeed ports to permit the passage of said influent therethrough.
 14. Themethod as defined in claim 13, further comprising the step ofperiodically discharging at least part of said flocculent from each ofsaid troughs into a holding tank disposed within said central hub. 15.The method as defined in claim 13, further comprising circulating saidinfluent within an influent supply chamber in fluid communication withsaid feed ports, wherein said influent supply chamber continuouslyreceives a supply of said influent from an influent source.
 16. Themethod as defined in claim 15, wherein said influent supply chamber islocated within said central hub and wherein said influent is circulatedwithin said influent supply chamber in a first direction and iscirculated within said container, after passage through said feed ports,in a second direction opposite said first direction.
 17. The method asdefined in claim 16, wherein said influent source is a bioreactorlocated upstream from said clarifier.
 18. The method as defined in claim17, further comprising mixing in said influent supply chamber a firststream of said influent comprising dissolved gas and a second stream ofsaid influent comprising dispersed gas.
 19. The method as defined inclaim 14, wherein said holding tank is in fluid communication with abioreactor located upstream from said clarifier and wherein said methodfurther comprises recycling a portion of said influent to said holdingtank.
 20. The method as defined in claim 19, further comprisingconveying sediments from a bottom portion of said conveyor to saidholding tank.
 21. The method as defined in claim 3, further comprisingadjusting the position of said scraper blade relative to an uppersurface of said beach.
 22. The method as defined in claim 14, whereinsaid flocculent collected in each of said troughs comprises returnactivated sludge and waste activated sludge and wherein said methodfurther comprises discharging said return activated sludge from saidtroughs into said holding tank and discharging said waste activatedsludge from said troughs to a location separate from said holding tank.23. The method as defined in claim 14, wherein said flocculent isdischarged from each of said troughs into said holding tanksequentially.
 24. The method as defined in claim 23, further comprisingmaintaining a hydraulic head difference between said troughs and saidholding tank, whereby said flocculent periodically flows from each ofsaid troughs into said holding tank without the use of pumps.
 25. Themethod as defined in claim 24, wherein each of said troughs comprises aflocculent discharge port proximate said central hub and wherein saidclarifier further comprises a rotatable ring having a plurality ofspaced-apart flocculent outlet ports, said method further comprisingrotating said rotatable ring around said hub to periodically bring saiddischarge port into at least partial alignment with one of said outletports to permit passage of flocculent therethrough into said holdingtank.
 26. The method as defined in claim 12, wherein said scraper bladeis supported for rotational movement by a leading support arm and atrailing supports arm and wherein said step of vertically displacingsaid scraper blade comprises adjusting the angular distance between saidsupport arms in the vicinity of each of said troughs.
 27. The method asdefined in claim 26, further comprising maintaining said supports armsin a rotational plane extending above the plane of rotation of saidscraper blade.
 28. A method of treating liquid influent in a circularclarifier having a container for holding said influent and at least onetrough extending at approximately the fill level of said influent withinsaid container, said method comprising: (a) introducing said influentinto a treatment region of said container in the vicinity of saidtrough; (b) causing a fraction of said influent comprising separablematter to form a surface layer of flocculent in a flotation subzone ofsaid treatment region; and (c) confining said flocculent within saidflotation subzone and gradually decreasing the volume of said flotationsubzone to cause said flocculent to rise above said fill level andgently spill into said trough without substantially disrupting saidflocculent, wherein said clarifier comprises a rotatable flocculenthandling assembly and wherein said step of gradually decreasing thevolume of said flotation subzone comprises rotating said flocculenthandling assembly through said treatment region, wherein rotation ofsaid flocculent handling assembly in said treatment region increases theconcentration of said flocculent in said flotation subzone, wherein saidflocculent handling assembly further comprises a scraper blade extendingupwardly from said beach, wherein said influent is introduced into saidcontainer continuously, wherein said clarifier comprises a plurality ofradially-spaced apart troughs and a plurality of separate treatmentregions, each of said treatment regions being defined between anadjacent pair of said troughs, wherein said influent is sequentiallyintroduced into said treatment regions in a timed sequence such thatsaid flocculent is substantially quiescent in at least some of saidflotation subzones in advance of the direction of rotation of saidflocculent handling assembly, wherein said scraper blade traversessubstantially all of the exposed surface of said treatment regions as itrotates within said container, the method further comprising verticallydisplacing said scraper blade in the vicinity of each of said troughs toenable said scraper blade to pass thereover and then descend into thenext-in-sequence one of said treatment regions, wherein said containeris defined between a central hub and a peripheral wall of saidclarifier, and wherein each of said troughs extends radially within saidcontainer at spaced locations, said central hub having a plurality offeed ports formed therein at spaced locations, wherein the step ofintroducing influent into said treatment regions in a timed sequencecomprises rotating a first rotatable ring around said hub, said ringhaving a plurality of influent inlet ports which are sequentiallybrought into at least partial register with said feed ports to permitthe passage of said influent therethrough, the method further comprisingthe step of periodically discharging at least part of said flocculentfrom each of said troughs into a holding tank disposed within saidcentral hub, wherein said flocculent collected in each of said troughscomprises return activated sludge and waste activated sludge and whereinsaid method further comprises discharging said return activated sludgefrom said troughs into said holding tank and discharging said wasteactivated sludge from said troughs to a location separate from saidholding tank.
 29. A method of treating liquid influent in a circularclarifier having a container for holding said influent and at least onetrough extending at approximately the fill level of said influent withinsaid container, said method comprising: (a) introducing said influentinto a treatment region of said container in the vicinity of saidtrough; (b) causing a fraction of said influent comprising separablematter to form a surface layer of flocculent in a flotation subzone ofsaid treatment region; and (c) confining said flocculent within saidflotation subzone and gradually decreasing the volume of said flotationsubzone to cause said flocculent to rise above said fill level andgently spill into said trough without substantially disrupting saidflocculent, wherein said clarifier comprises a rotatable flocculenthandling assembly and wherein said step of gradually decreasing thevolume of said flotation subzone comprises rotating said flocculenthandling assembly through said treatment region, wherein rotation ofsaid flocculent handling assembly in said treatment region increases theconcentration of said flocculent in said flotation subzone, wherein saidflocculent handling assembly further comprises a scraper blade extendingupwardly from said beach, wherein said influent is introduced into saidcontainer continuously, wherein said clarifier comprises a plurality ofradially-spaced apart troughs and a plurality of separate treatmentregions, each of said treatment regions being defined between anadjacent pair of said troughs, wherein said influent is sequentiallyintroduced into said treatment regions in a timed sequence such thatsaid flocculent is substantially quiescent in at least some of saidflotation subzones in advance of the direction of rotation of saidflocculent handling assembly, wherein said scraper blade traversessubstantially all of the exposed surface of said treatment regions as itrotates within said container, the method further comprising verticallydisplacing said scraper blade in the vicinity of each of said troughs toenable said scraper blade to pass thereover and then descend into thenext-in-sequence one of said treatment regions, wherein said containeris defined between a central hub and a peripheral wall of saidclarifier, and wherein each of said troughs extends radially within saidcontainer at spaced locations, said central hub having a plurality offeed ports formed therein at spaced locations, wherein the step ofintroducing influent into said treatment regions in a timed sequencecomprises rotating a first rotatable ring around said hub, said ringhaving a plurality of influent inlet ports which are sequentiallybrought into at least partial register with said feed ports to permitthe passage of said influent therethrough, the method further comprisingthe step of periodically discharging at least part of said flocculentfrom each of said troughs into a holding tank disposed within saidcentral hub, wherein said flocculent is discharged from each of saidtroughs into said holding tank sequentially, the method furthercomprising maintaining a hydraulic head difference between said troughsand said holding tank, whereby said flocculent periodically flows fromeach of said troughs into said holding tank without the use of pumps,wherein each of said troughs comprises a flocculent discharge portproximate said central hub and wherein said clarifier further comprisesa rotatable ring having a plurality of spaced-apart flocculent outletports, said method further comprising rotating said rotatable ringaround said hub to periodically bring said discharge port into at leastpartial alignment with one of said outlet ports to permit passage offlocculent therethrough into said holding tank.
 30. A method of treatingliquid influent in a circular clarifier having a container for holdingsaid influent and at least one trough extending at approximately thefill level of said influent within said container, said methodcomprising: (a) introducing said influent into a treatment region ofsaid container in the vicinity of said trough; (b) causing a fraction ofsaid influent comprising separable matter to form a surface layer offlocculent in a flotation subzone of said treatment region; and (c)confining said flocculent within said flotation subzone and graduallydecreasing the volume of said flotation subzone to cause said flocculentto rise above said fill level and gently spill into said trough withoutsubstantially disrupting said flocculent, wherein said clarifiercomprises a rotatable flocculent handling assembly and wherein said stepof gradually decreasing the volume of said flotation subzone comprisesrotating said flocculent handling assembly through said treatmentregion, wherein rotation of said flocculent handling assembly in saidtreatment region increases the concentration of said flocculent in saidflotation subzone, wherein said flocculent handling assembly furthercomprises a scraper blade extending upwardly from said beach, whereinsaid influent is introduced into said container continuously, whereinsaid clarifier comprises a plurality of radially-spaced apart troughsand a plurality of separate treatment regions, each of said treatmentregions being defined between an adjacent pair of said troughs, whereinsaid influent is sequentially introduced into said treatment regions ina timed sequence such that said flocculent is substantially quiescent inat least some of said flotation subzones in advance of the direction ofrotation of said flocculent handling assembly, wherein said scraperblade traverses substantially all of the exposed surface of saidtreatment regions as it rotates within said container, the methodfurther comprising vertically displacing said scraper blade in thevicinity of each of said troughs to enable said scraper blade to passthereover and then descend into the next-in-sequence one of saidtreatment regions, wherein said scraper blade is supported forrotational movement by a leading support arm and a trailing supports armand wherein said step of vertically displacing said scraper bladecomprises adjusting the angular distance between said support arms inthe vicinity of each of said troughs.
 31. The method as defined in claim30, further comprising maintaining said supports arms in a rotationalplane extending above the plane of rotation of said scraper blade.